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Message-ID: <5614F67C.3060003@oracle.com>
Date: Wed, 07 Oct 2015 18:39:56 +0800
From: Bob Liu <bob.liu@...cle.com>
To: Roger Pau Monné <roger.pau@...rix.com>
CC: xen-devel@...ts.xen.org, david.vrabel@...rix.com,
linux-kernel@...r.kernel.org, konrad.wilk@...cle.com,
felipe.franciosi@...rix.com, axboe@...com, hch@...radead.org,
avanzini.arianna@...il.com, rafal.mielniczuk@...rix.com,
boris.ostrovsky@...cle.com, jonathan.davies@...rix.com
Subject: Re: [PATCH v3 6/9] xen/blkfront: negotiate the number of hw queues/rings
with backend
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@...cle.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.
>
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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