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

[Bob Liu <bob.liu@xxxxxxxxxx>]

On 10/05/2015 10:40 PM, Roger Pau Monné wrote:
> 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...

Will update.

> 
>>
>> Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
>> ---
>>  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.
> 

The difficult part is how to return the right message?

>> +    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.
> 

Will update all above comments.

>> +
>>      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?
> 

Then the default value is 0, multi-queue isn't enabled by default.

>> +            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;
>>  
>>
> 

-- 
Regards,
-Bob

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