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Date: Tue, 19 Aug 2014 21:11:13 +0530
From: Kashyap Desai <kashyap.desai@...gotech.com>
To: Christoph Hellwig <hch@....de>,
James Bottomley <James.Bottomley@...senpartnership.com>,
linux-scsi@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>,
Bart Van Assche <bvanassche@...ionio.com>,
Mike Christie <michaelc@...wisc.edu>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Robert Elliott <Elliott@...com>, Webb Scales <webbnh@...com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/14] scsi: add support for a blk-mq based I/O path.
On Tue, Aug 19, 2014 at 3:51 AM, Kashyap Desai
<kashyap.desai@...gotech.com> wrote:
>
> > -----Original Message-----
> > From: linux-scsi-owner@...r.kernel.org [mailto:linux-scsi-
> > owner@...r.kernel.org] On Behalf Of Christoph Hellwig
> > Sent: Friday, July 18, 2014 3:43 PM
> > To: James Bottomley; linux-scsi@...r.kernel.org
> > Cc: Jens Axboe; Bart Van Assche; Mike Christie; Martin K. Petersen;
> Robert
> > Elliott; Webb Scales; linux-kernel@...r.kernel.org
> > Subject: [PATCH 13/14] scsi: add support for a blk-mq based I/O path.
> >
> > This patch adds support for an alternate I/O path in the scsi midlayer
> which
> > uses the blk-mq infrastructure instead of the legacy request code.
> >
> > Use of blk-mq is fully transparent to drivers, although for now a host
> > template field is provided to opt out of blk-mq usage in case any
> unforseen
> > incompatibilities arise.
> >
> > In general replacing the legacy request code with blk-mq is a simple and
> > mostly mechanical transformation. The biggest exception is the new code
> > that deals with the fact the I/O submissions in blk-mq must happen from
> > process context, which slightly complicates the I/O completion handler.
> > The second biggest differences is that blk-mq is build around the
> concept of
> > preallocated requests that also include driver specific data, which in
> SCSI
> > context means the scsi_cmnd structure. This completely avoids dynamic
> > memory allocations for the fast path through I/O submission.
> >
> > Due the preallocated requests the MQ code path exclusively uses the
> host-
> > wide shared tag allocator instead of a per-LUN one. This only affects
> drivers
> > actually using the block layer provided tag allocator instead of their
> own.
> > Unlike the old path blk-mq always provides a tag, although drivers don't
> have
> > to use it.
> >
> > For now the blk-mq path is disable by defauly and must be enabled using
> the
> > "use_blk_mq" module parameter. Once the remaining work in the block
> > layer to make blk-mq more suitable for slow devices is complete I hope
> to
> > make it the default and eventually even remove the old code path.
> >
> > Based on the earlier scsi-mq prototype by Nicholas Bellinger.
> >
> > Thanks to Bart Van Assche and Robert Elliot for testing, benchmarking
> and
> > various sugestions and code contributions.
> >
> > Signed-off-by: Christoph Hellwig <hch@....de>
> > Reviewed-by: Hannes Reinecke <hare@...e.de>
> > Reviewed-by: Webb Scales <webbnh@...com>
> > Acked-by: Jens Axboe <axboe@...nel.dk>
> > Tested-by: Bart Van Assche <bvanassche@....org>
> > Tested-by: Robert Elliott <elliott@...com>
> > ---
> > drivers/scsi/hosts.c | 35 +++-
> > drivers/scsi/scsi.c | 5 +-
> > drivers/scsi/scsi_lib.c | 464
> > ++++++++++++++++++++++++++++++++++++++++------
> > drivers/scsi/scsi_priv.h | 3 +
> > drivers/scsi/scsi_scan.c | 5 +-
> > drivers/scsi/scsi_sysfs.c | 2 +
> > include/scsi/scsi_host.h | 18 +-
> > include/scsi/scsi_tcq.h | 28 ++-
> > 8 files changed, 488 insertions(+), 72 deletions(-)
> >
> > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c index
> 0632eee..6de80e3
> > 100644
> > --- a/drivers/scsi/hosts.c
> > +++ b/drivers/scsi/hosts.c
> > @@ -213,9 +213,24 @@ int scsi_add_host_with_dma(struct Scsi_Host
> > *shost, struct device *dev,
> > goto fail;
> > }
> >
> > + if (shost_use_blk_mq(shost)) {
> > + error = scsi_mq_setup_tags(shost);
> > + if (error)
> > + goto fail;
> > + }
> > +
> > + /*
> > + * Note that we allocate the freelist even for the MQ case for
> now,
> > + * as we need a command set aside for scsi_reset_provider. Having
> > + * the full host freelist and one command available for that is a
> > + * little heavy-handed, but avoids introducing a special allocator
> > + * just for this. Eventually the structure of scsi_reset_provider
> > + * will need a major overhaul.
> > + */
> > error = scsi_setup_command_freelist(shost);
> > if (error)
> > - goto fail;
> > + goto out_destroy_tags;
> > +
> >
> > if (!shost->shost_gendev.parent)
> > shost->shost_gendev.parent = dev ? dev : &platform_bus;
> > @@ -226,7 +241,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost,
> > struct device *dev,
> >
> > error = device_add(&shost->shost_gendev);
> > if (error)
> > - goto out;
> > + goto out_destroy_freelist;
> >
> > pm_runtime_set_active(&shost->shost_gendev);
> > pm_runtime_enable(&shost->shost_gendev);
> > @@ -279,8 +294,11 @@ int scsi_add_host_with_dma(struct Scsi_Host
> > *shost, struct device *dev,
> > device_del(&shost->shost_dev);
> > out_del_gendev:
> > device_del(&shost->shost_gendev);
> > - out:
> > + out_destroy_freelist:
> > scsi_destroy_command_freelist(shost);
> > + out_destroy_tags:
> > + if (shost_use_blk_mq(shost))
> > + scsi_mq_destroy_tags(shost);
> > fail:
> > return error;
> > }
> > @@ -309,8 +327,13 @@ static void scsi_host_dev_release(struct device
> > *dev)
> > }
> >
> > scsi_destroy_command_freelist(shost);
> > - if (shost->bqt)
> > - blk_free_tags(shost->bqt);
> > + if (shost_use_blk_mq(shost)) {
> > + if (shost->tag_set.tags)
> > + scsi_mq_destroy_tags(shost);
> > + } else {
> > + if (shost->bqt)
> > + blk_free_tags(shost->bqt);
> > + }
> >
> > kfree(shost->shost_data);
> >
> > @@ -436,6 +459,8 @@ struct Scsi_Host *scsi_host_alloc(struct
> > scsi_host_template *sht, int privsize)
> > else
> > shost->dma_boundary = 0xffffffff;
> >
> > + shost->use_blk_mq = scsi_use_blk_mq && !shost->hostt-
> > >disable_blk_mq;
> > +
> > device_initialize(&shost->shost_gendev);
> > dev_set_name(&shost->shost_gendev, "host%d", shost->host_no);
> > shost->shost_gendev.bus = &scsi_bus_type; diff --git
> > a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c index 3dde8a3..013709f
> 100644
> > --- a/drivers/scsi/scsi.c
> > +++ b/drivers/scsi/scsi.c
> > @@ -805,7 +805,7 @@ void scsi_adjust_queue_depth(struct scsi_device
> > *sdev, int tagged, int tags)
> > * is more IO than the LLD's can_queue (so there are not enuogh
> > * tags) request_fn's host queue ready check will handle it.
> > */
> > - if (!sdev->host->bqt) {
> > + if (!shost_use_blk_mq(sdev->host) && !sdev->host->bqt) {
> > if (blk_queue_tagged(sdev->request_queue) &&
> > blk_queue_resize_tags(sdev->request_queue, tags) != 0)
> > goto out;
> > @@ -1361,6 +1361,9 @@ MODULE_LICENSE("GPL");
> > module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
> > MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");
> >
> > +bool scsi_use_blk_mq = false;
> > +module_param_named(use_blk_mq, scsi_use_blk_mq, bool, S_IWUSR |
> > +S_IRUGO);
> > +
> > static int __init init_scsi(void)
> > {
> > int error;
> > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index
> > bbd7a0a..9c44392 100644
> > --- a/drivers/scsi/scsi_lib.c
> > +++ b/drivers/scsi/scsi_lib.c
> > @@ -1,5 +1,6 @@
> > /*
> > - * scsi_lib.c Copyright (C) 1999 Eric Youngdale
> > + * Copyright (C) 1999 Eric Youngdale
> > + * Copyright (C) 2014 Christoph Hellwig
> > *
> > * SCSI queueing library.
> > * Initial versions: Eric Youngdale (eric@...ante.org).
> > @@ -20,6 +21,7 @@
> > #include <linux/delay.h>
> > #include <linux/hardirq.h>
> > #include <linux/scatterlist.h>
> > +#include <linux/blk-mq.h>
> >
> > #include <scsi/scsi.h>
> > #include <scsi/scsi_cmnd.h>
> > @@ -113,6 +115,16 @@ scsi_set_blocked(struct scsi_cmnd *cmd, int reason)
> > }
> > }
> >
> > +static void scsi_mq_requeue_cmd(struct scsi_cmnd *cmd) {
> > + struct scsi_device *sdev = cmd->device;
> > + struct request_queue *q = cmd->request->q;
> > +
> > + blk_mq_requeue_request(cmd->request);
> > + blk_mq_kick_requeue_list(q);
> > + put_device(&sdev->sdev_gendev);
> > +}
> > +
> > /**
> > * __scsi_queue_insert - private queue insertion
> > * @cmd: The SCSI command being requeued @@ -150,6 +162,10 @@ static
> > void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
> > * before blk_cleanup_queue() finishes.
> > */
> > cmd->result = 0;
> > + if (q->mq_ops) {
> > + scsi_mq_requeue_cmd(cmd);
> > + return;
> > + }
> > spin_lock_irqsave(q->queue_lock, flags);
> > blk_requeue_request(q, cmd->request);
> > kblockd_schedule_work(&device->requeue_work);
> > @@ -308,6 +324,14 @@ void scsi_device_unbusy(struct scsi_device *sdev)
> > atomic_dec(&sdev->device_busy);
> > }
> >
> > +static void scsi_kick_queue(struct request_queue *q) {
> > + if (q->mq_ops)
> > + blk_mq_start_hw_queues(q);
> > + else
> > + blk_run_queue(q);
> > +}
> > +
> > /*
> > * Called for single_lun devices on IO completion. Clear
> starget_sdev_user,
> > * and call blk_run_queue for all the scsi_devices on the target - @@
> -332,7
> > +356,7 @@ static void scsi_single_lun_run(struct scsi_device
> *current_sdev)
> > * but in most cases, we will be first. Ideally, each LU on the
> > * target would get some limited time or requests on the target.
> > */
> > - blk_run_queue(current_sdev->request_queue);
> > + scsi_kick_queue(current_sdev->request_queue);
> >
> > spin_lock_irqsave(shost->host_lock, flags);
> > if (starget->starget_sdev_user)
> > @@ -345,7 +369,7 @@ static void scsi_single_lun_run(struct scsi_device
> > *current_sdev)
> > continue;
> >
> > spin_unlock_irqrestore(shost->host_lock, flags);
> > - blk_run_queue(sdev->request_queue);
> > + scsi_kick_queue(sdev->request_queue);
> > spin_lock_irqsave(shost->host_lock, flags);
> >
> > scsi_device_put(sdev);
> > @@ -435,7 +459,7 @@ static void scsi_starved_list_run(struct Scsi_Host
> > *shost)
> > continue;
> > spin_unlock_irqrestore(shost->host_lock, flags);
> >
> > - blk_run_queue(slq);
> > + scsi_kick_queue(slq);
> > blk_put_queue(slq);
> >
> > spin_lock_irqsave(shost->host_lock, flags); @@ -466,7
> > +490,10 @@ static void scsi_run_queue(struct request_queue *q)
> > if (!list_empty(&sdev->host->starved_list))
> > scsi_starved_list_run(sdev->host);
> >
> > - blk_run_queue(q);
> > + if (q->mq_ops)
> > + blk_mq_start_stopped_hw_queues(q, false);
> > + else
> > + blk_run_queue(q);
> > }
> >
> > void scsi_requeue_run_queue(struct work_struct *work) @@ -564,25
> > +591,72 @@ static struct scatterlist *scsi_sg_alloc(unsigned int nents,
> gfp_t
> > gfp_mask)
> > return mempool_alloc(sgp->pool, gfp_mask); }
> >
> > -static void scsi_free_sgtable(struct scsi_data_buffer *sdb)
> > +static void scsi_free_sgtable(struct scsi_data_buffer *sdb, bool mq)
> > {
> > - __sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, false,
> > scsi_sg_free);
> > + if (mq && sdb->table.nents <= SCSI_MAX_SG_SEGMENTS)
> > + return;
> > + __sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, mq,
> > scsi_sg_free);
> > }
> >
> > static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents,
> > - gfp_t gfp_mask)
> > + gfp_t gfp_mask, bool mq)
> > {
> > + struct scatterlist *first_chunk = NULL;
> > int ret;
> >
> > BUG_ON(!nents);
> >
> > + if (mq) {
> > + if (nents <= SCSI_MAX_SG_SEGMENTS) {
> > + sdb->table.nents = nents;
> > + sg_init_table(sdb->table.sgl, sdb->table.nents);
> > + return 0;
> > + }
> > + first_chunk = sdb->table.sgl;
> > + }
> > +
> > ret = __sg_alloc_table(&sdb->table, nents,
> > SCSI_MAX_SG_SEGMENTS,
> > - NULL, gfp_mask, scsi_sg_alloc);
> > + first_chunk, gfp_mask, scsi_sg_alloc);
> > if (unlikely(ret))
> > - scsi_free_sgtable(sdb);
> > + scsi_free_sgtable(sdb, mq);
> > return ret;
> > }
> >
> > +static void scsi_uninit_cmd(struct scsi_cmnd *cmd) {
> > + if (cmd->request->cmd_type == REQ_TYPE_FS) {
> > + struct scsi_driver *drv = scsi_cmd_to_driver(cmd);
> > +
> > + if (drv->uninit_command)
> > + drv->uninit_command(cmd);
> > + }
> > +}
> > +
> > +static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd) {
> > + if (cmd->sdb.table.nents)
> > + scsi_free_sgtable(&cmd->sdb, true);
> > + if (cmd->request->next_rq && cmd->request->next_rq->special)
> > + scsi_free_sgtable(cmd->request->next_rq->special, true);
> > + if (scsi_prot_sg_count(cmd))
> > + scsi_free_sgtable(cmd->prot_sdb, true); }
> > +
> > +static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd) {
> > + struct scsi_device *sdev = cmd->device;
> > + unsigned long flags;
> > +
> > + BUG_ON(list_empty(&cmd->list));
> > +
> > + scsi_mq_free_sgtables(cmd);
> > + scsi_uninit_cmd(cmd);
> > +
> > + spin_lock_irqsave(&sdev->list_lock, flags);
> > + list_del_init(&cmd->list);
> > + spin_unlock_irqrestore(&sdev->list_lock, flags); }
> > +
> > /*
> > * Function: scsi_release_buffers()
> > *
> > @@ -602,19 +676,19 @@ static int scsi_alloc_sgtable(struct
> scsi_data_buffer
> > *sdb, int nents, static void scsi_release_buffers(struct scsi_cmnd
> *cmd) {
> > if (cmd->sdb.table.nents)
> > - scsi_free_sgtable(&cmd->sdb);
> > + scsi_free_sgtable(&cmd->sdb, false);
> >
> > memset(&cmd->sdb, 0, sizeof(cmd->sdb));
> >
> > if (scsi_prot_sg_count(cmd))
> > - scsi_free_sgtable(cmd->prot_sdb);
> > + scsi_free_sgtable(cmd->prot_sdb, false);
> > }
> >
> > static void scsi_release_bidi_buffers(struct scsi_cmnd *cmd) {
> > struct scsi_data_buffer *bidi_sdb = cmd->request->next_rq-
> > >special;
> >
> > - scsi_free_sgtable(bidi_sdb);
> > + scsi_free_sgtable(bidi_sdb, false);
> > kmem_cache_free(scsi_sdb_cache, bidi_sdb);
> > cmd->request->next_rq->special = NULL; } @@ -625,8 +699,6 @@
> > static bool scsi_end_request(struct request *req, int error,
> > struct scsi_cmnd *cmd = req->special;
> > struct scsi_device *sdev = cmd->device;
> > struct request_queue *q = sdev->request_queue;
> > - unsigned long flags;
> > -
> >
> > if (blk_update_request(req, error, bytes))
> > return true;
> > @@ -639,14 +711,38 @@ static bool scsi_end_request(struct request *req,
> > int error,
> > if (blk_queue_add_random(q))
> > add_disk_randomness(req->rq_disk);
> >
> > - spin_lock_irqsave(q->queue_lock, flags);
> > - blk_finish_request(req, error);
> > - spin_unlock_irqrestore(q->queue_lock, flags);
> > + if (req->mq_ctx) {
> > + /*
> > + * In the MQ case the command gets freed by
> > __blk_mq_end_io,
> > + * so we have to do all cleanup that depends on it
> earlier.
> > + *
> > + * We also can't kick the queues from irq context, so we
> > + * will have to defer it to a workqueue.
> > + */
> > + scsi_mq_uninit_cmd(cmd);
> > +
> > + __blk_mq_end_io(req, error);
> > +
> > + if (scsi_target(sdev)->single_lun ||
> > + !list_empty(&sdev->host->starved_list))
> > + kblockd_schedule_work(&sdev->requeue_work);
> > + else
> > + blk_mq_start_stopped_hw_queues(q, true);
> > +
> > + put_device(&sdev->sdev_gendev);
> > + } else {
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(q->queue_lock, flags);
> > + blk_finish_request(req, error);
> > + spin_unlock_irqrestore(q->queue_lock, flags);
> > +
> > + if (bidi_bytes)
> > + scsi_release_bidi_buffers(cmd);
> > + scsi_release_buffers(cmd);
> > + scsi_next_command(cmd);
> > + }
> >
> > - if (bidi_bytes)
> > - scsi_release_bidi_buffers(cmd);
> > - scsi_release_buffers(cmd);
> > - scsi_next_command(cmd);
> > return false;
> > }
> >
> > @@ -953,8 +1049,14 @@ void scsi_io_completion(struct scsi_cmnd *cmd,
> > unsigned int good_bytes)
> > /* Unprep the request and put it back at the head of the
> > queue.
> > * A new command will be prepared and issued.
> > */
> > - scsi_release_buffers(cmd);
> > - scsi_requeue_command(q, cmd);
> > + if (q->mq_ops) {
> > + cmd->request->cmd_flags &= ~REQ_DONTPREP;
> > + scsi_mq_uninit_cmd(cmd);
> > + scsi_mq_requeue_cmd(cmd);
> > + } else {
> > + scsi_release_buffers(cmd);
> > + scsi_requeue_command(q, cmd);
> > + }
> > break;
> > case ACTION_RETRY:
> > /* Retry the same command immediately */ @@ -976,9
> > +1078,8 @@ static int scsi_init_sgtable(struct request *req, struct
> > scsi_data_buffer *sdb,
> > * If sg table allocation fails, requeue request later.
> > */
> > if (unlikely(scsi_alloc_sgtable(sdb, req->nr_phys_segments,
> > - gfp_mask))) {
> > + gfp_mask, req->mq_ctx != NULL)))
> > return BLKPREP_DEFER;
> > - }
> >
> > /*
> > * Next, walk the list, and fill in the addresses and sizes of @@
> -
> > 1006,6 +1107,7 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t
> gfp_mask) {
> > struct scsi_device *sdev = cmd->device;
> > struct request *rq = cmd->request;
> > + bool is_mq = (rq->mq_ctx != NULL);
> > int error;
> >
> > BUG_ON(!rq->nr_phys_segments);
> > @@ -1015,15 +1117,19 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t
> > gfp_mask)
> > goto err_exit;
> >
> > if (blk_bidi_rq(rq)) {
> > - struct scsi_data_buffer *bidi_sdb = kmem_cache_zalloc(
> > - scsi_sdb_cache, GFP_ATOMIC);
> > - if (!bidi_sdb) {
> > - error = BLKPREP_DEFER;
> > - goto err_exit;
> > + if (!rq->q->mq_ops) {
> > + struct scsi_data_buffer *bidi_sdb =
> > + kmem_cache_zalloc(scsi_sdb_cache,
> > GFP_ATOMIC);
> > + if (!bidi_sdb) {
> > + error = BLKPREP_DEFER;
> > + goto err_exit;
> > + }
> > +
> > + rq->next_rq->special = bidi_sdb;
> > }
> >
> > - rq->next_rq->special = bidi_sdb;
> > - error = scsi_init_sgtable(rq->next_rq, bidi_sdb,
> > GFP_ATOMIC);
> > + error = scsi_init_sgtable(rq->next_rq,
> rq->next_rq->special,
> > + GFP_ATOMIC);
> > if (error)
> > goto err_exit;
> > }
> > @@ -1035,7 +1141,7 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t
> > gfp_mask)
> > BUG_ON(prot_sdb == NULL);
> > ivecs = blk_rq_count_integrity_sg(rq->q, rq->bio);
> >
> > - if (scsi_alloc_sgtable(prot_sdb, ivecs, gfp_mask)) {
> > + if (scsi_alloc_sgtable(prot_sdb, ivecs, gfp_mask, is_mq))
> {
> > error = BLKPREP_DEFER;
> > goto err_exit;
> > }
> > @@ -1049,13 +1155,16 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t
> > gfp_mask)
> > cmd->prot_sdb->table.nents = count;
> > }
> >
> > - return BLKPREP_OK ;
> > -
> > + return BLKPREP_OK;
> > err_exit:
> > - scsi_release_buffers(cmd);
> > - cmd->request->special = NULL;
> > - scsi_put_command(cmd);
> > - put_device(&sdev->sdev_gendev);
> > + if (is_mq) {
> > + scsi_mq_free_sgtables(cmd);
> > + } else {
> > + scsi_release_buffers(cmd);
> > + cmd->request->special = NULL;
> > + scsi_put_command(cmd);
> > + put_device(&sdev->sdev_gendev);
> > + }
> > return error;
> > }
> > EXPORT_SYMBOL(scsi_init_io);
> > @@ -1266,13 +1375,7 @@ out:
> >
> > static void scsi_unprep_fn(struct request_queue *q, struct request
> *req) {
> > - if (req->cmd_type == REQ_TYPE_FS) {
> > - struct scsi_cmnd *cmd = req->special;
> > - struct scsi_driver *drv = scsi_cmd_to_driver(cmd);
> > -
> > - if (drv->uninit_command)
> > - drv->uninit_command(cmd);
> > - }
> > + scsi_uninit_cmd(req->special);
> > }
> >
> > /*
> > @@ -1295,7 +1398,11 @@ static inline int scsi_dev_queue_ready(struct
> > request_queue *q,
> > * unblock after device_blocked iterates to zero
> > */
> > if (atomic_dec_return(&sdev->device_blocked) > 0) {
> > - blk_delay_queue(q, SCSI_QUEUE_DELAY);
> > + /*
> > + * For the MQ case we take care of this in the
> caller.
> > + */
> > + if (!q->mq_ops)
> > + blk_delay_queue(q, SCSI_QUEUE_DELAY);
> > goto out_dec;
> > }
> > SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev, @@
> > -1671,6 +1778,180 @@ out_delay:
> > blk_delay_queue(q, SCSI_QUEUE_DELAY); }
> >
> > +static inline int prep_to_mq(int ret)
> > +{
> > + switch (ret) {
> > + case BLKPREP_OK:
> > + return 0;
> > + case BLKPREP_DEFER:
> > + return BLK_MQ_RQ_QUEUE_BUSY;
> > + default:
> > + return BLK_MQ_RQ_QUEUE_ERROR;
> > + }
> > +}
> > +
> > +static int scsi_mq_prep_fn(struct request *req) {
> > + struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
> > + struct scsi_device *sdev = req->q->queuedata;
> > + struct Scsi_Host *shost = sdev->host;
> > + unsigned char *sense_buf = cmd->sense_buffer;
> > + struct scatterlist *sg;
> > +
> > + memset(cmd, 0, sizeof(struct scsi_cmnd));
> > +
> > + req->special = cmd;
> > +
> > + cmd->request = req;
> > + cmd->device = sdev;
> > + cmd->sense_buffer = sense_buf;
> > +
> > + cmd->tag = req->tag;
> > +
> > + req->cmd = req->__cmd;
> > + cmd->cmnd = req->cmd;
> > + cmd->prot_op = SCSI_PROT_NORMAL;
> > +
> > + INIT_LIST_HEAD(&cmd->list);
> > + INIT_DELAYED_WORK(&cmd->abort_work,
> > scmd_eh_abort_handler);
> > + cmd->jiffies_at_alloc = jiffies;
> > +
> > + /*
> > + * XXX: cmd_list lookups are only used by two drivers, try to get
> > + * rid of this list in common code.
> > + */
> > + spin_lock_irq(&sdev->list_lock);
> > + list_add_tail(&cmd->list, &sdev->cmd_list);
> > + spin_unlock_irq(&sdev->list_lock);
>
> Hi Chris,
>
> I am using scsi.mq.4 branch and doing profiling to find out possible
> improvement in low level driver to get benefit of SCSI.MQ. I am using
> LSI/Avago 12G MegaRaid Invader and total 12 SSDs (of 12Gpb/s).
> I have done some changes in "megaraid_sas" driver to gain from scsi.mq
> interface. I will send the list of changes some time later to get early
> feedback..
>
> I used this thread to reply as I found relevant patch to explain you
> better.
>
> Here are few data points - ( I used 4K Rand READ FIO-libaio load on Two
> socket Super micro server)
>
> If I use "null_blk" driver, I was able to get 1800K IOPs on my setup
> When I used "megaraid_sas" driver in loop back mode (FAKE READ/WRITE), I
> see below numbers.
> Keep the worker on Node-0, 1800K IOPs (similar to null_blk), but when I
> spread workers on Node-0 and Node-1, I see ~700K IOPS.
>
> Above experiment hint me that there may be some difference in SCSI.MQ
> compare to BLK-MQ.
>
> My original problem was - "12 Drives R0 cannot scale beyond 750K IOPS, but
> it goes upto 1200K IOPS if I keep workers on Node-0 using cpus_allowed
> parameter of fio"
>
> Lock stats data - Below data is for work load where I was not able to
> scale beyond 750K IOPS..
>
>
> --------------------------------------------------------------------------
> ------
> class name con-bounces contentions
> waittime-min waittime-max waittime-total waittime-avg acq-bounces
> acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg
> --------------------------------------------------------------------------
> --------------------------------------------------------------------------
> -------------------------------------------------------------------------
>
> &(&sdev->list_lock)->rlock: 2307248 2308395
> 0.07 158.89 10435357.44 4.52 3849400
> 3958002 0.04 26.02 1123671.56 0.28
> --------------------------
> &(&sdev->list_lock)->rlock 1105029
> [<ffffffff814ac980>] scsi_queue_rq+0x560/0x750
> &(&sdev->list_lock)->rlock 1203366
> [<ffffffff814abc97>] scsi_mq_uninit_cmd+0x47/0xb0
> --------------------------
> &(&sdev->list_lock)->rlock 1176271
> [<ffffffff814abc97>] scsi_mq_uninit_cmd+0x47/0xb0
> &(&sdev->list_lock)->rlock 1132124
> [<ffffffff814ac980>] scsi_queue_rq+0x560/0x750
>
>
>
> I read this comment and find that very few drivers are using this
> cmd_list. I think if we remove this cmd_list, performance will scale as I
> am seeing major contention in this lock.
> Just thought to ping you to see if this is known limitation for now or any
> plan to change this lock in near future ?
Additional info -
I tried after removing spinlock + list_add/del from scsi_mq_uninit()
and scsi_queue_rq(), IOPs are able to scale now upto 1100K (earlier
only 700K IOPS) which is almost similar to IO load running on single
Numa Node.
>
>
> ~ Kashyap
>
> > +
> > + sg = (void *)cmd + sizeof(struct scsi_cmnd) + shost->hostt-
> > >cmd_size;
> > + cmd->sdb.table.sgl = sg;
> > +
> > + if (scsi_host_get_prot(shost)) {
> > + cmd->prot_sdb = (void *)sg +
> > + shost->sg_tablesize * sizeof(struct scatterlist);
> > + memset(cmd->prot_sdb, 0, sizeof(struct scsi_data_buffer));
> > +
> > + cmd->prot_sdb->table.sgl =
> > + (struct scatterlist *)(cmd->prot_sdb + 1);
> > + }
> > +
> > + if (blk_bidi_rq(req)) {
> > + struct request *next_rq = req->next_rq;
> > + struct scsi_data_buffer *bidi_sdb =
> > blk_mq_rq_to_pdu(next_rq);
> > +
> > + memset(bidi_sdb, 0, sizeof(struct scsi_data_buffer));
> > + bidi_sdb->table.sgl =
> > + (struct scatterlist *)(bidi_sdb + 1);
> > +
> > + next_rq->special = bidi_sdb;
> > + }
> > +
> > + return scsi_setup_cmnd(sdev, req);
> > +}
> > +
> > +static void scsi_mq_done(struct scsi_cmnd *cmd) {
> > + trace_scsi_dispatch_cmd_done(cmd);
> > + blk_mq_complete_request(cmd->request);
> > +}
> > +
> > +static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request
> > +*req) {
> > + struct request_queue *q = req->q;
> > + struct scsi_device *sdev = q->queuedata;
> > + struct Scsi_Host *shost = sdev->host;
> > + struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
> > + int ret;
> > + int reason;
> > +
> > + ret = prep_to_mq(scsi_prep_state_check(sdev, req));
> > + if (ret)
> > + goto out;
> > +
> > + ret = BLK_MQ_RQ_QUEUE_BUSY;
> > + if (!get_device(&sdev->sdev_gendev))
> > + goto out;
> > +
> > + if (!scsi_dev_queue_ready(q, sdev))
> > + goto out_put_device;
> > + if (!scsi_target_queue_ready(shost, sdev))
> > + goto out_dec_device_busy;
> > + if (!scsi_host_queue_ready(q, shost, sdev))
> > + goto out_dec_target_busy;
> > +
> > + if (!(req->cmd_flags & REQ_DONTPREP)) {
> > + ret = prep_to_mq(scsi_mq_prep_fn(req));
> > + if (ret)
> > + goto out_dec_host_busy;
> > + req->cmd_flags |= REQ_DONTPREP;
> > + }
> > +
> > + scsi_init_cmd_errh(cmd);
> > + cmd->scsi_done = scsi_mq_done;
> > +
> > + reason = scsi_dispatch_cmd(cmd);
> > + if (reason) {
> > + scsi_set_blocked(cmd, reason);
> > + ret = BLK_MQ_RQ_QUEUE_BUSY;
> > + goto out_dec_host_busy;
> > + }
> > +
> > + return BLK_MQ_RQ_QUEUE_OK;
> > +
> > +out_dec_host_busy:
> > + atomic_dec(&shost->host_busy);
> > +out_dec_target_busy:
> > + if (scsi_target(sdev)->can_queue > 0)
> > + atomic_dec(&scsi_target(sdev)->target_busy);
> > +out_dec_device_busy:
> > + atomic_dec(&sdev->device_busy);
> > +out_put_device:
> > + put_device(&sdev->sdev_gendev);
> > +out:
> > + switch (ret) {
> > + case BLK_MQ_RQ_QUEUE_BUSY:
> > + blk_mq_stop_hw_queue(hctx);
> > + if (atomic_read(&sdev->device_busy) == 0 &&
> > + !scsi_device_blocked(sdev))
> > + blk_mq_delay_queue(hctx, SCSI_QUEUE_DELAY);
> > + break;
> > + case BLK_MQ_RQ_QUEUE_ERROR:
> > + /*
> > + * Make sure to release all allocated ressources when
> > + * we hit an error, as we will never see this command
> > + * again.
> > + */
> > + if (req->cmd_flags & REQ_DONTPREP)
> > + scsi_mq_uninit_cmd(cmd);
> > + break;
> > + default:
> > + break;
> > + }
> > + return ret;
> > +}
> > +
> > +static int scsi_init_request(void *data, struct request *rq,
> > + unsigned int hctx_idx, unsigned int request_idx,
> > + unsigned int numa_node)
> > +{
> > + struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
> > +
> > + cmd->sense_buffer = kzalloc_node(SCSI_SENSE_BUFFERSIZE,
> > GFP_KERNEL,
> > + numa_node);
> > + if (!cmd->sense_buffer)
> > + return -ENOMEM;
> > + return 0;
> > +}
> > +
> > +static void scsi_exit_request(void *data, struct request *rq,
> > + unsigned int hctx_idx, unsigned int request_idx) {
> > + struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
> > +
> > + kfree(cmd->sense_buffer);
> > +}
> > +
> > static u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost) {
> > struct device *host_dev;
> > @@ -1692,16 +1973,10 @@ static u64 scsi_calculate_bounce_limit(struct
> > Scsi_Host *shost)
> > return bounce_limit;
> > }
> >
> > -struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
> > - request_fn_proc *request_fn)
> > +static void __scsi_init_queue(struct Scsi_Host *shost, struct
> > +request_queue *q)
> > {
> > - struct request_queue *q;
> > struct device *dev = shost->dma_dev;
> >
> > - q = blk_init_queue(request_fn, NULL);
> > - if (!q)
> > - return NULL;
> > -
> > /*
> > * this limit is imposed by hardware restrictions
> > */
> > @@ -1732,7 +2007,17 @@ struct request_queue *__scsi_alloc_queue(struct
> > Scsi_Host *shost,
> > * blk_queue_update_dma_alignment() later.
> > */
> > blk_queue_dma_alignment(q, 0x03);
> > +}
> >
> > +struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
> > + request_fn_proc *request_fn)
> > +{
> > + struct request_queue *q;
> > +
> > + q = blk_init_queue(request_fn, NULL);
> > + if (!q)
> > + return NULL;
> > + __scsi_init_queue(shost, q);
> > return q;
> > }
> > EXPORT_SYMBOL(__scsi_alloc_queue);
> > @@ -1753,6 +2038,55 @@ struct request_queue *scsi_alloc_queue(struct
> > scsi_device *sdev)
> > return q;
> > }
> >
> > +static struct blk_mq_ops scsi_mq_ops = {
> > + .map_queue = blk_mq_map_queue,
> > + .queue_rq = scsi_queue_rq,
> > + .complete = scsi_softirq_done,
> > + .timeout = scsi_times_out,
> > + .init_request = scsi_init_request,
> > + .exit_request = scsi_exit_request,
> > +};
> > +
> > +struct request_queue *scsi_mq_alloc_queue(struct scsi_device *sdev) {
> > + sdev->request_queue = blk_mq_init_queue(&sdev->host-
> > >tag_set);
> > + if (IS_ERR(sdev->request_queue))
> > + return NULL;
> > +
> > + sdev->request_queue->queuedata = sdev;
> > + __scsi_init_queue(sdev->host, sdev->request_queue);
> > + return sdev->request_queue;
> > +}
> > +
> > +int scsi_mq_setup_tags(struct Scsi_Host *shost) {
> > + unsigned int cmd_size, sgl_size, tbl_size;
> > +
> > + tbl_size = shost->sg_tablesize;
> > + if (tbl_size > SCSI_MAX_SG_SEGMENTS)
> > + tbl_size = SCSI_MAX_SG_SEGMENTS;
> > + sgl_size = tbl_size * sizeof(struct scatterlist);
> > + cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size +
> > sgl_size;
> > + if (scsi_host_get_prot(shost))
> > + cmd_size += sizeof(struct scsi_data_buffer) + sgl_size;
> > +
> > + memset(&shost->tag_set, 0, sizeof(shost->tag_set));
> > + shost->tag_set.ops = &scsi_mq_ops;
> > + shost->tag_set.nr_hw_queues = 1;
> > + shost->tag_set.queue_depth = shost->can_queue;
> > + shost->tag_set.cmd_size = cmd_size;
> > + shost->tag_set.numa_node = NUMA_NO_NODE;
> > + shost->tag_set.flags = BLK_MQ_F_SHOULD_MERGE |
> > BLK_MQ_F_SG_MERGE;
> > + shost->tag_set.driver_data = shost;
> > +
> > + return blk_mq_alloc_tag_set(&shost->tag_set);
> > +}
> > +
> > +void scsi_mq_destroy_tags(struct Scsi_Host *shost) {
> > + blk_mq_free_tag_set(&shost->tag_set);
> > +}
> > +
> > /*
> > * Function: scsi_block_requests()
> > *
> > @@ -2498,9 +2832,13 @@ scsi_internal_device_block(struct scsi_device
> > *sdev)
> > * block layer from calling the midlayer with this device's
> > * request queue.
> > */
> > - spin_lock_irqsave(q->queue_lock, flags);
> > - blk_stop_queue(q);
> > - spin_unlock_irqrestore(q->queue_lock, flags);
> > + if (q->mq_ops) {
> > + blk_mq_stop_hw_queues(q);
> > + } else {
> > + spin_lock_irqsave(q->queue_lock, flags);
> > + blk_stop_queue(q);
> > + spin_unlock_irqrestore(q->queue_lock, flags);
> > + }
> >
> > return 0;
> > }
> > @@ -2546,9 +2884,13 @@ scsi_internal_device_unblock(struct scsi_device
> > *sdev,
> > sdev->sdev_state != SDEV_OFFLINE)
> > return -EINVAL;
> >
> > - spin_lock_irqsave(q->queue_lock, flags);
> > - blk_start_queue(q);
> > - spin_unlock_irqrestore(q->queue_lock, flags);
> > + if (q->mq_ops) {
> > + blk_mq_start_stopped_hw_queues(q, false);
> > + } else {
> > + spin_lock_irqsave(q->queue_lock, flags);
> > + blk_start_queue(q);
> > + spin_unlock_irqrestore(q->queue_lock, flags);
> > + }
> >
> > return 0;
> > }
> > diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h index
> > a45d1c2..12b8e1b 100644
> > --- a/drivers/scsi/scsi_priv.h
> > +++ b/drivers/scsi/scsi_priv.h
> > @@ -88,6 +88,9 @@ extern void scsi_next_command(struct scsi_cmnd
> > *cmd); extern void scsi_io_completion(struct scsi_cmnd *, unsigned
> int);
> > extern void scsi_run_host_queues(struct Scsi_Host *shost); extern
> struct
> > request_queue *scsi_alloc_queue(struct scsi_device *sdev);
> > +extern struct request_queue *scsi_mq_alloc_queue(struct scsi_device
> > +*sdev); extern int scsi_mq_setup_tags(struct Scsi_Host *shost); extern
> > +void scsi_mq_destroy_tags(struct Scsi_Host *shost);
> > extern int scsi_init_queue(void);
> > extern void scsi_exit_queue(void);
> > struct request_queue;
> > diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c index
> > 4a6e4ba..b91cfaf 100644
> > --- a/drivers/scsi/scsi_scan.c
> > +++ b/drivers/scsi/scsi_scan.c
> > @@ -273,7 +273,10 @@ static struct scsi_device *scsi_alloc_sdev(struct
> > scsi_target *starget,
> > */
> > sdev->borken = 1;
> >
> > - sdev->request_queue = scsi_alloc_queue(sdev);
> > + if (shost_use_blk_mq(shost))
> > + sdev->request_queue = scsi_mq_alloc_queue(sdev);
> > + else
> > + sdev->request_queue = scsi_alloc_queue(sdev);
> > if (!sdev->request_queue) {
> > /* release fn is set up in scsi_sysfs_device_initialise,
> so
> > * have to free and put manually here */ diff --git
> > a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index
> deef063..6c9227f
> > 100644
> > --- a/drivers/scsi/scsi_sysfs.c
> > +++ b/drivers/scsi/scsi_sysfs.c
> > @@ -333,6 +333,7 @@ store_shost_eh_deadline(struct device *dev, struct
> > device_attribute *attr,
> >
> > static DEVICE_ATTR(eh_deadline, S_IRUGO | S_IWUSR,
> > show_shost_eh_deadline, store_shost_eh_deadline);
> >
> > +shost_rd_attr(use_blk_mq, "%d\n");
> > shost_rd_attr(unique_id, "%u\n");
> > shost_rd_attr(cmd_per_lun, "%hd\n");
> > shost_rd_attr(can_queue, "%hd\n");
> > @@ -352,6 +353,7 @@ show_host_busy(struct device *dev, struct
> > device_attribute *attr, char *buf) static DEVICE_ATTR(host_busy,
> S_IRUGO,
> > show_host_busy, NULL);
> >
> > static struct attribute *scsi_sysfs_shost_attrs[] = {
> > + &dev_attr_use_blk_mq.attr,
> > &dev_attr_unique_id.attr,
> > &dev_attr_host_busy.attr,
> > &dev_attr_cmd_per_lun.attr,
> > diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h index
> > 5e8ebc1..ba20347 100644
> > --- a/include/scsi/scsi_host.h
> > +++ b/include/scsi/scsi_host.h
> > @@ -7,6 +7,7 @@
> > #include <linux/workqueue.h>
> > #include <linux/mutex.h>
> > #include <linux/seq_file.h>
> > +#include <linux/blk-mq.h>
> > #include <scsi/scsi.h>
> >
> > struct request_queue;
> > @@ -510,6 +511,9 @@ struct scsi_host_template {
> > */
> > unsigned int cmd_size;
> > struct scsi_host_cmd_pool *cmd_pool;
> > +
> > + /* temporary flag to disable blk-mq I/O path */
> > + bool disable_blk_mq;
> > };
> >
> > /*
> > @@ -580,7 +584,10 @@ struct Scsi_Host {
> > * Area to keep a shared tag map (if needed, will be
> > * NULL if not).
> > */
> > - struct blk_queue_tag *bqt;
> > + union {
> > + struct blk_queue_tag *bqt;
> > + struct blk_mq_tag_set tag_set;
> > + };
> >
> > atomic_t host_busy; /* commands actually active on
> low-
> > level */
> > atomic_t host_blocked;
> > @@ -672,6 +679,8 @@ struct Scsi_Host {
> > /* The controller does not support WRITE SAME */
> > unsigned no_write_same:1;
> >
> > + unsigned use_blk_mq:1;
> > +
> > /*
> > * Optional work queue to be utilized by the transport
> > */
> > @@ -772,6 +781,13 @@ static inline int scsi_host_in_recovery(struct
> > Scsi_Host *shost)
> > shost->tmf_in_progress;
> > }
> >
> > +extern bool scsi_use_blk_mq;
> > +
> > +static inline bool shost_use_blk_mq(struct Scsi_Host *shost) {
> > + return shost->use_blk_mq;
> > +}
> > +
> > extern int scsi_queue_work(struct Scsi_Host *, struct work_struct *);
> > extern void scsi_flush_work(struct Scsi_Host *);
> >
> > diff --git a/include/scsi/scsi_tcq.h b/include/scsi/scsi_tcq.h index
> > 81dd12e..cdcc90b 100644
> > --- a/include/scsi/scsi_tcq.h
> > +++ b/include/scsi/scsi_tcq.h
> > @@ -67,7 +67,8 @@ static inline void scsi_activate_tcq(struct
> scsi_device
> > *sdev, int depth)
> > if (!sdev->tagged_supported)
> > return;
> >
> > - if (!blk_queue_tagged(sdev->request_queue))
> > + if (!shost_use_blk_mq(sdev->host) &&
> > + blk_queue_tagged(sdev->request_queue))
> > blk_queue_init_tags(sdev->request_queue, depth,
> > sdev->host->bqt);
> >
> > @@ -80,7 +81,8 @@ static inline void scsi_activate_tcq(struct
> scsi_device
> > *sdev, int depth)
> > **/
> > static inline void scsi_deactivate_tcq(struct scsi_device *sdev, int
> depth) {
> > - if (blk_queue_tagged(sdev->request_queue))
> > + if (!shost_use_blk_mq(sdev->host) &&
> > + blk_queue_tagged(sdev->request_queue))
> > blk_queue_free_tags(sdev->request_queue);
> > scsi_adjust_queue_depth(sdev, 0, depth); } @@ -108,6 +110,15 @@
> > static inline int scsi_populate_tag_msg(struct scsi_cmnd *cmd, char
> *msg)
> > return 0;
> > }
> >
> > +static inline struct scsi_cmnd *scsi_mq_find_tag(struct Scsi_Host
> *shost,
> > + unsigned int hw_ctx, int tag)
> > +{
> > + struct request *req;
> > +
> > + req = blk_mq_tag_to_rq(shost->tag_set.tags[hw_ctx], tag);
> > + return req ? (struct scsi_cmnd *)req->special : NULL; }
> > +
> > /**
> > * scsi_find_tag - find a tagged command by device
> > * @SDpnt: pointer to the ScSI device
> > @@ -118,10 +129,12 @@ static inline int scsi_populate_tag_msg(struct
> > scsi_cmnd *cmd, char *msg)
> > **/
> > static inline struct scsi_cmnd *scsi_find_tag(struct scsi_device *sdev,
> int tag)
> > {
> > -
> > struct request *req;
> >
> > if (tag != SCSI_NO_TAG) {
> > + if (shost_use_blk_mq(sdev->host))
> > + return scsi_mq_find_tag(sdev->host, 0, tag);
> > +
> > req = blk_queue_find_tag(sdev->request_queue, tag);
> > return req ? (struct scsi_cmnd *)req->special : NULL;
> > }
> > @@ -130,6 +143,7 @@ static inline struct scsi_cmnd *scsi_find_tag(struct
> > scsi_device *sdev, int tag)
> > return sdev->current_cmnd;
> > }
> >
> > +
> > /**
> > * scsi_init_shared_tag_map - create a shared tag map
> > * @shost: the host to share the tag map among all devices
> > @@ -138,6 +152,12 @@ static inline struct scsi_cmnd
> *scsi_find_tag(struct
> > scsi_device *sdev, int tag) static inline int
> scsi_init_shared_tag_map(struct
> > Scsi_Host *shost, int depth) {
> > /*
> > + * We always have a shared tag map around when using blk-mq.
> > + */
> > + if (shost_use_blk_mq(shost))
> > + return 0;
> > +
> > + /*
> > * If the shared tag map isn't already initialized, do it now.
> > * This saves callers from having to check ->bqt when setting up
> > * devices on the shared host (for libata) @@ -165,6 +185,8 @@
> static
> > inline struct scsi_cmnd *scsi_host_find_tag(struct Scsi_Host *shost,
> > struct request *req;
> >
> > if (tag != SCSI_NO_TAG) {
> > + if (shost_use_blk_mq(shost))
> > + return scsi_mq_find_tag(shost, 0, tag);
> > req = blk_map_queue_find_tag(shost->bqt, tag);
> > return req ? (struct scsi_cmnd *)req->special : NULL;
> > }
> > --
> > 1.9.1
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the
> > body of a message to majordomo@...r.kernel.org More majordomo info at
> > http://vger.kernel.org/majordomo-info.html
--
Device Driver Developer @ Avagotech
Kashyap D. Desai
Note - my new email address
kashyap.desai@...gotech.com
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