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



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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