Re: [PATCH v3 6/9] xen/blkfront: negotiate the number of hw queues/rings with backend

["Roger Pau Monné" <roger.pau@citrix.com>]

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@oracle.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;
>  
>