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

[Bob Liu]

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.

>> +			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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