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

Bob Liu
2015-11-04T01:11:25Z

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@oracle.com>
>> ---
>> 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