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Message-ID: <FF7FC980937D6342B9D289F5F3C7C2625B5670CD@SHSMSX103.ccr.corp.intel.com>
Date: Tue, 28 Mar 2017 02:15:03 +0000
From: "Liu, Changpeng" <changpeng.liu@...el.com>
To: Stefan Hajnoczi <stefanha@...il.com>
CC: "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"hch@....de" <hch@....de>,
"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>
Subject: RE: [PATCH] virtio-blk: add DISCARD support to virtio-blk driver
> -----Original Message-----
> From: Stefan Hajnoczi [mailto:stefanha@...il.com]
> Sent: Tuesday, March 28, 2017 4:20 AM
> To: Liu, Changpeng <changpeng.liu@...el.com>
> Cc: virtio-dev@...ts.oasis-open.org; virtualization@...ts.linux-foundation.org; linux-
> kernel@...r.kernel.org; hch@....de; qemu-devel@...gnu.org
> Subject: Re: [PATCH] virtio-blk: add DISCARD support to virtio-blk driver
>
> On Tue, Mar 28, 2017 at 04:39:25PM +0800, Changpeng Liu wrote:
> > Currently virtio-blk driver does not provide discard feature flag, so the
> > filesystems which built on top of the block device will not send discard
> > command. This is okay for HDD backend, but it will impact the performance
> > for SSD backend.
> >
> > Add a feature flag VIRTIO_BLK_F_DISCARD and command
> VIRTIO_BLK_T_DISCARD
> > to extend exist virtio-blk protocol. virtio-blk protocol uses a single
> > 8 bytes descriptor containing type,reserved and sector, currently Linux
> > uses the reserved field as IO priority, here we also re-use the reserved
> > field as number of discard sectors.
> >
> > Signed-off-by: Changpeng Liu <changpeng.liu@...el.com>
> > ---
> > drivers/block/virtio_blk.c | 38 +++++++++++++++++++++++++++++---------
> > include/uapi/linux/virtio_blk.h | 12 ++++++++++--
> > 2 files changed, 39 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 1d4c9f8..550cfe7 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -241,6 +241,9 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> > case REQ_OP_FLUSH:
> > type = VIRTIO_BLK_T_FLUSH;
> > break;
> > + case REQ_OP_DISCARD:
> > + type = VIRTIO_BLK_T_DISCARD;
> > + break;
> > case REQ_OP_SCSI_IN:
> > case REQ_OP_SCSI_OUT:
> > type = VIRTIO_BLK_T_SCSI_CMD;
> > @@ -256,16 +259,24 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> > vbr->out_hdr.type = cpu_to_virtio32(vblk->vdev, type);
> > vbr->out_hdr.sector = type ?
> > 0 : cpu_to_virtio64(vblk->vdev, blk_rq_pos(req));
> > - vbr->out_hdr.ioprio = cpu_to_virtio32(vblk->vdev, req_get_ioprio(req));
> > + vbr->out_hdr.u.ioprio = cpu_to_virtio32(vblk->vdev, req_get_ioprio(req));
> >
> > blk_mq_start_request(req);
> >
> > - num = blk_rq_map_sg(hctx->queue, req, vbr->sg);
> > - if (num) {
> > - if (rq_data_dir(req) == WRITE)
> > - vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev,
> VIRTIO_BLK_T_OUT);
> > - else
> > - vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev,
> VIRTIO_BLK_T_IN);
> > + if (type == VIRTIO_BLK_T_DISCARD) {
> > + vbr->out_hdr.u.discard_nr_sectors = cpu_to_virtio32(vblk->vdev,
> > +
> blk_rq_sectors(req));
> > + num = 0;
> > + } else {
> > + num = blk_rq_map_sg(hctx->queue, req, vbr->sg);
> > + if (num) {
> > + if (rq_data_dir(req) == WRITE)
> > + vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev,
> > +
> VIRTIO_BLK_T_OUT);
> > + else
> > + vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev,
> > +
> VIRTIO_BLK_T_IN);
> > + }
> > }
> >
> > spin_lock_irqsave(&vblk->vqs[qid].lock, flags);
> > @@ -775,6 +786,15 @@ static int virtblk_probe(struct virtio_device *vdev)
> > if (!err && opt_io_size)
> > blk_queue_io_opt(q, blk_size * opt_io_size);
> >
> > + if (virtio_has_feature(vdev, VIRTIO_BLK_F_DISCARD)) {
> > + q->limits.discard_zeroes_data = 0;
> > + q->limits.discard_alignment = blk_size;
> > + q->limits.discard_granularity = blk_size;
> > + blk_queue_max_discard_sectors(q, UINT_MAX);
> > + blk_queue_max_discard_segments(q, 1);
> > + queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
> > + }
>
> Please add configuration space fields for these limits. Looking at the
> virtio-scsi block limits code in QEMU's scsi_disk_emulate_inquiry() I
> can see that the hypervisor has useful values that it wants to
> communicate. They shouldn't be hardcoded to blk_size.
Yes, move discard related parameters to configuration space make sense.
>
> > +
> > virtio_device_ready(vdev);
> >
> > device_add_disk(&vdev->dev, vblk->disk);
> > @@ -882,14 +902,14 @@ static int virtblk_restore(struct virtio_device *vdev)
> > VIRTIO_BLK_F_SCSI,
> > #endif
> > VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY,
> VIRTIO_BLK_F_CONFIG_WCE,
> > - VIRTIO_BLK_F_MQ,
> > + VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
> > }
> > ;
> > static unsigned int features[] = {
> > VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX,
> VIRTIO_BLK_F_GEOMETRY,
> > VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
> > VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY,
> VIRTIO_BLK_F_CONFIG_WCE,
> > - VIRTIO_BLK_F_MQ,
> > + VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
> > };
> >
> > static struct virtio_driver virtio_blk = {
> > diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
> > index 9ebe4d9..d608649 100644
> > --- a/include/uapi/linux/virtio_blk.h
> > +++ b/include/uapi/linux/virtio_blk.h
> > @@ -38,6 +38,7 @@
> > #define VIRTIO_BLK_F_BLK_SIZE 6 /* Block size of disk is available*/
> > #define VIRTIO_BLK_F_TOPOLOGY 10 /* Topology information is
> available */
> > #define VIRTIO_BLK_F_MQ 12 /* support more than one vq */
> > +#define VIRTIO_BLK_F_DISCARD 13 /* DISCARD command is supported
> */
> >
> > /* Legacy feature bits */
> > #ifndef VIRTIO_BLK_NO_LEGACY
> > @@ -114,6 +115,9 @@ struct virtio_blk_config {
> > /* Get device ID command */
> > #define VIRTIO_BLK_T_GET_ID 8
> >
> > +/* Discard command */
> > +#define VIRTIO_BLK_T_DISCARD 16
> > +
> > #ifndef VIRTIO_BLK_NO_LEGACY
> > /* Barrier before this op. */
> > #define VIRTIO_BLK_T_BARRIER 0x80000000
> > @@ -127,8 +131,12 @@ struct virtio_blk_config {
> > struct virtio_blk_outhdr {
> > /* VIRTIO_BLK_T* */
> > __virtio32 type;
> > - /* io priority. */
> > - __virtio32 ioprio;
> > + union {
> > + /* io priority. */
> > + __virtio32 ioprio;
> > + /* discard number of sectors */
> > + __virtio32 discard_nr_sectors;
> > + } u;
>
> DISCARD commands have no io priority? Perhaps it's better to add an
> extended header.
What I think now is that, keep the ioprio field, and let DISCARD command has input data buffers, 16 bytes aligned descriptor for each
DISCARD segment(can support mult-range feature), and this is also aligned with SCSI and NVMe specification.
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