Re: [PATCH v4 08/10] xen/blkback: get the number of hardware queues/rings from blkfront

Konrad Rzeszutek Wilk
2015-11-05T02:37:46Z

On Mon, Nov 02, 2015 at 12:21:44PM +0800, Bob Liu wrote:
> Backend advertises "multi-queue-max-queues" to front, then get the negotiated

s/then/so/
> number from "multi-queue-num-queues" wrote by blkfront.
s/wrote/written/

>
> Signed-off-by: Bob Liu <bob.liu@oracle.com>
> ---
> drivers/block/xen-blkback/blkback.c | 11 +++++++++++
> drivers/block/xen-blkback/common.h | 1 +
> drivers/block/xen-blkback/xenbus.c | 35 +++++++++++++++++++++++++++++------
> 3 files changed, 41 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index eaf7ec0..107cc4a 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -83,6 +83,11 @@ module_param_named(max_persistent_grants, xen_blkif_max_pgrants, int, 0644);
> MODULE_PARM_DESC(max_persistent_grants,
> "Maximum number of grants to map persistently");
>
> +unsigned int xenblk_max_queues;

Do you want a default value?

> +module_param_named(max_queues, xenblk_max_queues, uint, 0644);
> +MODULE_PARM_DESC(max_queues,
> + "Maximum number of hardware queues per virtual disk");
> +
> /*
> * Maximum order of pages to be used for the shared ring between front and
> * backend, 4KB page granularity is used.
> @@ -1478,6 +1483,12 @@ static int __init xen_blkif_init(void)
> xen_blkif_max_ring_order = XENBUS_MAX_RING_PAGE_ORDER;
> }
>
> + /* Allow as many queues as there are CPUs if user has not
> + * specified a value.

That should be part of the module_param actually.
> + */
> + if (xenblk_max_queues == 0)
> + xenblk_max_queues = num_online_cpus();
> +
> rc = xen_blkif_interface_init();
> if (rc)
> goto failed_init;
> diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
> index 4de1326..fb28b91 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -45,6 +45,7 @@
> #include <xen/interface/io/protocols.h>
>
> extern unsigned int xen_blkif_max_ring_order;
> +extern unsigned int xenblk_max_queues;
> /*
> * This is the maximum number of segments that would be allowed in indirect
> * requests. This value will also be passed to the frontend.
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index ac4b458..cafbadd 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -181,12 +181,6 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
> INIT_LIST_HEAD(&blkif->persistent_purge_list);
> INIT_WORK(&blkif->persistent_purge_work, xen_blkbk_unmap_purged_grants);
>
> - blkif->nr_rings = 1;
> - if (xen_blkif_alloc_rings(blkif)) {
> - kmem_cache_free(xen_blkif_cachep, blkif);
> - return ERR_PTR(-ENOMEM);
> - }
> -
> return blkif;
> }
>
> @@ -606,6 +600,14 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
> goto fail;
> }
>
> + /* Multi-queue: write how many queues are supported by the backend. */
> + err = xenbus_printf(XBT_NIL, dev->nodename,
> + "multi-queue-max-queues", "%u", xenblk_max_queues);
> + if (err) {
> + pr_warn("Error writing multi-queue-num-queues\n");
> + goto fail;

Why fail? If we can't - then we can't and won't advertise this support.
We should still be able to work, right?

That is how the ''max-ring-page-order' does it below.
> + }
> +
> /* setup back pointer */
> be->blkif->be = be;
>
> @@ -997,6 +999,7 @@ static int connect_ring(struct backend_info *be)
> char *xspath;
> size_t xspathsize;
> const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */
> + unsigned int requested_num_queues = 0;
>
> pr_debug("%s %s\n", __func__, dev->otherend);
>
> @@ -1024,6 +1027,26 @@ static int connect_ring(struct backend_info *be)
> be->blkif->vbd.feature_gnt_persistent = pers_grants;
> be->blkif->vbd.overflow_max_grants = 0;
>
> + /*
> + * Read the number of hardware queues from frontend.
> + */
> + err = xenbus_scanf(XBT_NIL, dev->otherend, "multi-queue-num-queues", "%u", &requested_num_queues);

Please split this in two lines.

> + if (err < 0) {
> + requested_num_queues = 1;
> + } else {
> + if (requested_num_queues > xenblk_max_queues
> + || requested_num_queues == 0) {
> + /* buggy or malicious guest */
> + xenbus_dev_fatal(dev, err,
> + "guest requested %u queues, exceeding the maximum of %u.",
> + requested_num_queues, xenblk_max_queues);
> + return -1;
> + }
> + }
> + be->blkif->nr_rings = requested_num_queues;
> + if (xen_blkif_alloc_rings(be->blkif))
> + return -ENOMEM;
> +
> pr_info("nr_rings:%d protocol %d (%s) %s\n", be->blkif->nr_rings,
> be->blkif->blk_protocol, protocol,
> pers_grants ? "persistent grants" : "");
> --
> 1.8.3.1
>