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Message-ID: <56128BC0.1090109@citrix.com>
Date: Mon, 5 Oct 2015 16:40:00 +0200
From: Roger Pau Monné <roger.pau@...rix.com>
To: Bob Liu <bob.liu@...cle.com>, <xen-devel@...ts.xen.org>
CC: <david.vrabel@...rix.com>, <linux-kernel@...r.kernel.org>,
<konrad.wilk@...cle.com>, <felipe.franciosi@...rix.com>,
<axboe@...com>, <hch@...radead.org>, <avanzini.arianna@...il.com>,
<rafal.mielniczuk@...rix.com>, <boris.ostrovsky@...cle.com>,
<jonathan.davies@...rix.com>
Subject: Re: [PATCH v3 6/9] xen/blkfront: negotiate the number of hw
queues/rings with backend
El 05/09/15 a les 14.39, Bob Liu ha escrit:
> The max number of hardware queues for xen/blkfront is set by parameter
> 'max_queues', while the number xen/blkback supported is notified through
> xenstore("multi-queue-max-queues").
>
> The negotiated number was the smaller one, and was written back to
> xen/blkback as "multi-queue-num-queues".
I would write this in present instead of past, I think it's clearer:
The negotiated number _is_ the smaller...
>
> Signed-off-by: Bob Liu <bob.liu@...cle.com>
> ---
> drivers/block/xen-blkfront.c | 142 ++++++++++++++++++++++++++++++++----------
> 1 file changed, 108 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 1cae76b..1aa66c9 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -107,6 +107,10 @@ static unsigned int xen_blkif_max_ring_order;
> module_param_named(max_ring_page_order, xen_blkif_max_ring_order, int, S_IRUGO);
> MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the shared ring");
>
> +static unsigned int xen_blkif_max_queues;
> +module_param_named(max_queues, xen_blkif_max_queues, uint, S_IRUGO);
> +MODULE_PARM_DESC(max_queues, "Maximum number of hardware queues/rings per virtual disk");
> +
> #define BLK_RING_SIZE(dinfo) __CONST_RING_SIZE(blkif, PAGE_SIZE * (dinfo)->pages_per_ring)
> #define BLK_MAX_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE * XENBUS_MAX_RING_PAGES)
> /*
> @@ -114,6 +118,7 @@ MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the
> * characters are enough. Define to 20 to keep consist with backend.
> */
> #define RINGREF_NAME_LEN (20)
> +#define QUEUE_NAME_LEN (12)
>
> /*
> * Per-ring info.
> @@ -687,7 +692,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
>
> memset(&dinfo->tag_set, 0, sizeof(dinfo->tag_set));
> dinfo->tag_set.ops = &blkfront_mq_ops;
> - dinfo->tag_set.nr_hw_queues = 1;
> + dinfo->tag_set.nr_hw_queues = dinfo->nr_rings;
> dinfo->tag_set.queue_depth = BLK_RING_SIZE(dinfo);
> dinfo->tag_set.numa_node = NUMA_NO_NODE;
> dinfo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
> @@ -1350,6 +1355,51 @@ fail:
> return err;
> }
>
> +static int write_per_ring_nodes(struct xenbus_transaction xbt,
> + struct blkfront_ring_info *rinfo, const char *dir)
> +{
> + int err, i;
> + const char *message = NULL;
> + struct blkfront_dev_info *dinfo = rinfo->dinfo;
> +
> + if (dinfo->pages_per_ring == 1) {
> + err = xenbus_printf(xbt, dir, "ring-ref", "%u", rinfo->ring_ref[0]);
> + if (err) {
> + message = "writing ring-ref";
> + goto abort_transaction;
> + }
> + pr_info("%s: write ring-ref:%d\n", dir, rinfo->ring_ref[0]);
> + } else {
> + for (i = 0; i < dinfo->pages_per_ring; i++) {
> + char ring_ref_name[RINGREF_NAME_LEN];
> +
> + snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
> + err = xenbus_printf(xbt, dir, ring_ref_name,
> + "%u", rinfo->ring_ref[i]);
> + if (err) {
> + message = "writing ring-ref";
> + goto abort_transaction;
> + }
> + pr_info("%s: write ring-ref:%d\n", dir, rinfo->ring_ref[i]);
> + }
> + }
> +
> + err = xenbus_printf(xbt, dir, "event-channel", "%u", rinfo->evtchn);
> + if (err) {
> + message = "writing event-channel";
> + goto abort_transaction;
> + }
> + pr_info("%s: write event-channel:%d\n", dir, rinfo->evtchn);
> +
> + return 0;
> +
> +abort_transaction:
> + xenbus_transaction_end(xbt, 1);
The transaction is not started inside of the helper, so I would prefer
it to be ended in the same function where it is started. This should
just return the error and the caller should end the transaction.
> + if (message)
> + xenbus_dev_fatal(dinfo->xbdev, err, "%s", message);
> +
> + return err;
> +}
>
> /* Common code used when first setting up, and when resuming. */
> static int talk_to_blkback(struct xenbus_device *dev,
> @@ -1386,45 +1436,51 @@ again:
> goto out;
> }
>
> + if (dinfo->pages_per_ring > 1) {
> + err = xenbus_printf(xbt, dev->nodename, "ring-page-order", "%u",
> + ring_page_order);
> + if (err) {
> + message = "writing ring-page-order";
> + goto abort_transaction;
> + }
> + }
> +
> + /* We already got the number of queues in _probe */
> if (dinfo->nr_rings == 1) {
> rinfo = &dinfo->rinfo[0];
>
> - if (dinfo->pages_per_ring == 1) {
> - err = xenbus_printf(xbt, dev->nodename,
> - "ring-ref", "%u", rinfo->ring_ref[0]);
> - if (err) {
> - message = "writing ring-ref";
> - goto abort_transaction;
> - }
> - } else {
> - err = xenbus_printf(xbt, dev->nodename,
> - "ring-page-order", "%u", ring_page_order);
> - if (err) {
> - message = "writing ring-page-order";
> - goto abort_transaction;
> - }
> -
> - for (i = 0; i < dinfo->pages_per_ring; i++) {
> - char ring_ref_name[RINGREF_NAME_LEN];
> + err = write_per_ring_nodes(xbt, &dinfo->rinfo[0], dev->nodename);
> + if (err)
> + goto out;
> + } else {
> + char *path;
> + size_t pathsize;
>
> - snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
> - err = xenbus_printf(xbt, dev->nodename, ring_ref_name,
> - "%u", rinfo->ring_ref[i]);
> - if (err) {
> - message = "writing ring-ref";
> - goto abort_transaction;
> - }
> - }
> - }
> - err = xenbus_printf(xbt, dev->nodename,
> - "event-channel", "%u", rinfo->evtchn);
> + err = xenbus_printf(xbt, dev->nodename, "multi-queue-num-queues", "%u",
> + dinfo->nr_rings);
> if (err) {
> - message = "writing event-channel";
> + message = "writing multi-queue-num-queues";
> goto abort_transaction;
> }
> - } else {
> - /* Not supported at this stage */
> - goto abort_transaction;
> +
> + pathsize = strlen(dev->nodename) + QUEUE_NAME_LEN;
> + path = kzalloc(pathsize, GFP_KERNEL);
kmalloc seems better here, since you are memseting it below in order to
reuse it.
> + if (!path) {
> + err = -ENOMEM;
> + message = "ENOMEM while writing ring references";
> + goto abort_transaction;
> + }
> +
> + for (i = 0; i < dinfo->nr_rings; i++) {
> + memset(path, 0, pathsize);
> + snprintf(path, pathsize, "%s/queue-%u", dev->nodename, i);
> + err = write_per_ring_nodes(xbt, &dinfo->rinfo[i], path);
> + if (err) {
> + kfree(path);
> + goto out;
> + }
> + }
> + kfree(path);
> }
>
> err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
> @@ -1480,6 +1536,7 @@ static int blkfront_probe(struct xenbus_device *dev,
> int err, vdevice, r_index;
> struct blkfront_dev_info *dinfo;
> struct blkfront_ring_info *rinfo;
> + unsigned int back_max_queues = 0;
>
> /* FIXME: Use dynamic device id if this is not set. */
> err = xenbus_scanf(XBT_NIL, dev->nodename,
> @@ -1534,7 +1591,17 @@ static int blkfront_probe(struct xenbus_device *dev,
> dinfo->vdevice = vdevice;
> dinfo->connected = BLKIF_STATE_DISCONNECTED;
>
> - dinfo->nr_rings = 1;
> + /* Check if backend supports multiple queues */
> + err = xenbus_scanf(XBT_NIL, dinfo->xbdev->otherend,
> + "multi-queue-max-queues", "%u", &back_max_queues);
> + if (err < 0)
> + back_max_queues = 1;
> +
> + dinfo->nr_rings = min(back_max_queues, xen_blkif_max_queues);
> + if (dinfo->nr_rings <= 0)
> + dinfo->nr_rings = 1;
> + pr_info("dinfo->nr_rings:%u, backend support max-queues:%u\n", dinfo->nr_rings, back_max_queues);
^ pr_debug ^ supports
And I would also print the number of queues that are going to be used.
> +
> dinfo->rinfo = kzalloc(sizeof(*rinfo) * dinfo->nr_rings, GFP_KERNEL);
> if (!dinfo->rinfo) {
> xenbus_dev_fatal(dev, -ENOMEM, "allocating ring_info structure");
> @@ -2257,6 +2324,7 @@ static struct xenbus_driver blkfront_driver = {
> static int __init xlblk_init(void)
> {
> int ret;
> + int nr_cpus = num_online_cpus();
>
> if (!xen_domain())
> return -ENODEV;
> @@ -2267,6 +2335,12 @@ static int __init xlblk_init(void)
> xen_blkif_max_ring_order = 0;
> }
>
> + if (xen_blkif_max_queues > nr_cpus) {
Shouldn't there be a default value for xen_blkif_max_queues if the user
hasn't set the parameter on the command line?
> + pr_info("Invalid max_queues (%d), will use default max: %d.\n",
> + xen_blkif_max_queues, nr_cpus);
> + xen_blkif_max_queues = nr_cpus;
> + }
> +
> if (!xen_has_pv_disk_devices())
> return -ENODEV;
>
>
--
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