Re: [PATCH v4 05/10] xen/blkfront: negotiate number of queues/rings to be used with backend

From: Konrad Rzeszutek Wilk
Date: Tue Nov 03 2015 - 20:54:11 EST

On Wed, Nov 04, 2015 at 09:11:10AM +0800, Bob Liu wrote:
>
> On 11/04/2015 04:40 AM, Konrad Rzeszutek Wilk wrote:
> > On Mon, Nov 02, 2015 at 12:21:41PM +0800, Bob Liu wrote:
> >> The number of hardware queues for xen/blkfront is set by parameter
> >> 'max_queues'(default 4), while the max value xen/blkback supported is notified
> >> through xenstore("multi-queue-max-queues").
> >
> > That is not right.
> >
> > s/The number/The max number/
> >
> > The second part: ",while the max value xen/blkback supported is..". I think
> > you are trying to say: "it is also capped by the max value that
> > the xen/blkback exposes through XenStore key 'multi-queue-max-queues'.
> >
> >>
> >> The negotiated number is the smaller one and would be written back to xenstore
> >> as "multi-queue-num-queues", blkback need to read this negotiated number.
> >
> > s/blkback need to read/blkback needs to read this/
> >
> >>
> >> Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
> >> ---
> >> drivers/block/xen-blkfront.c | 166 +++++++++++++++++++++++++++++++------------
> >> 1 file changed, 120 insertions(+), 46 deletions(-)
> >>
> >> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> >> index 8cc5995..23096d7 100644
> >> --- a/drivers/block/xen-blkfront.c
> >> +++ b/drivers/block/xen-blkfront.c
> >> @@ -98,6 +98,10 @@ static unsigned int xen_blkif_max_segments = 32;
> >> module_param_named(max, xen_blkif_max_segments, int, S_IRUGO);
> >> MODULE_PARM_DESC(max, "Maximum amount of segments in indirect requests (default is 32)");
> >>
> >> +static unsigned int xen_blkif_max_queues = 4;
> >> +module_param_named(max_queues, xen_blkif_max_queues, uint, S_IRUGO);
> >> +MODULE_PARM_DESC(max_queues, "Maximum number of hardware queues/rings used per virtual disk");
> >> +
> >> /*
> >> * Maximum order of pages to be used for the shared ring between front and
> >> * backend, 4KB page granularity is used.
> >> @@ -113,6 +117,7 @@ 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)
> >
> > Little bit of documentation please. Why 12? Why not 31415 for example?
> > I presume it is 'queue-%u' and since so that is 7 + 10 (UINT_MAX is
> > 4294967295) = 17!
> >
> >
> >>
> >> /*
> >> * Per-ring info.
> >> @@ -695,7 +700,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
> >>
> >> memset(&info->tag_set, 0, sizeof(info->tag_set));
> >> info->tag_set.ops = &blkfront_mq_ops;
> >> - info->tag_set.nr_hw_queues = 1;
> >> + info->tag_set.nr_hw_queues = info->nr_rings;
> >> info->tag_set.queue_depth = BLK_RING_SIZE(info);
> >> info->tag_set.numa_node = NUMA_NO_NODE;
> >> info->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
> >> @@ -1352,6 +1357,51 @@ fail:
> >> return err;
> >> }
> >>
> >> +static int write_per_ring_nodes(struct xenbus_transaction xbt,
> >> + struct blkfront_ring_info *rinfo, const char *dir)
> >> +{
> >> + int err, i;
> >
> > Please make 'i' be an unsigned int. Especially as you are using '%u' in the snprintf.
> >
> >
> >> + const char *message = NULL;
> >> + struct blkfront_info *info = rinfo->dev_info;
> >> +
> >> + if (info->nr_ring_pages == 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]);
> >
> > Ewww. No.
> >
> >> + } else {
> >> + for (i = 0; i < info->nr_ring_pages; 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]);
> >
> > No no please.
> >
> >> + }
> >> + }
> >> +
> >> + err = xenbus_printf(xbt, dir, "event-channel", "%u", rinfo->evtchn);
> >
> > That is not right.
> >
> > That only creates one. But the blkif.h says (And the example agrees)
> > that there are N 'event-channel' for N-rings.
> >
> > Shouldn't this be part of the above loop?
> >
>
> No, this loop is only for per-ring each with "multipage".
>
> The loop you want is..
>
> >> + if (err) {
> >> + message = "writing event-channel";
> >> + goto abort_transaction;
> >> + }
> >> + pr_info("%s: write event-channel:%d\n", dir, rinfo->evtchn);
> >
> > Please no.
> >
> >> +
> >> + return 0;
> >> +
> >> +abort_transaction:
> >> + xenbus_transaction_end(xbt, 1);
> >> + if (message)
> >> + xenbus_dev_fatal(info->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,
> >> @@ -1362,7 +1412,6 @@ static int talk_to_blkback(struct xenbus_device *dev,
> >> int err, i;
> >> unsigned int max_page_order = 0;
> >> unsigned int ring_page_order = 0;
> >> - struct blkfront_ring_info *rinfo;
> >>
> >> err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
> >> "max-ring-page-order", "%u", &max_page_order);
> >> @@ -1374,7 +1423,8 @@ static int talk_to_blkback(struct xenbus_device *dev,
> >> }
> >>
> >> for (i = 0; i < info->nr_rings; i++) {
> >> - rinfo = &info->rinfo[i];
> >> + struct blkfront_ring_info *rinfo = &info->rinfo[i];
> >> +
> >> /* Create shared ring, alloc event channel. */
> >> err = setup_blkring(dev, rinfo);
> >> if (err)
> >> @@ -1388,45 +1438,51 @@ again:
> >> goto destroy_blkring;
> >> }
> >>
> >> - if (info->nr_rings == 1) {
> >> - rinfo = &info->rinfo[0];
> >> - if (info->nr_ring_pages == 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;
> >> - }
> >> + if (info->nr_ring_pages > 1) {
> >> + 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 < info->nr_ring_pages; i++) {
> >> - char ring_ref_name[RINGREF_NAME_LEN];
> >> + /* We already got the number of queues/rings in _probe */
> >> + if (info->nr_rings == 1) {
> >> + err = write_per_ring_nodes(xbt, &info->rinfo[0], dev->nodename);
> >> + if (err)
> >> + goto destroy_blkring;
> >> + } 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",
> >> + info->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 = kmalloc(pathsize, GFP_KERNEL);
> >> + if (!path) {
> >> + err = -ENOMEM;
> >> + message = "ENOMEM while writing ring references";
> >> + goto abort_transaction;
> >> + }
> >> +
> >> + for (i = 0; i < info->nr_rings; i++) {
>
> at here.

Please document that then. That is a bit confusing.
>
> >> + memset(path, 0, pathsize);
> >> + snprintf(path, pathsize, "%s/queue-%u", dev->nodename, i);
> >> + err = write_per_ring_nodes(xbt, &info->rinfo[i], path);
> >> + if (err) {
> >> + kfree(path);
> >> + goto destroy_blkring;
> >> + }
> >> + }
> >> + kfree(path);
> >> }
> >> +
>
> Will update all other comments.
>
> --
> Regards,
> -Bob
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