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Date: Wed, 25 Nov 2015 12:58:36 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Bob Liu <bob.liu@...cle.com>
Cc: xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
roger.pau@...rix.com, felipe.franciosi@...rix.com, axboe@...com,
avanzini.arianna@...il.com, rafal.mielniczuk@...rix.com,
jonathan.davies@...rix.com, david.vrabel@...rix.com
Subject: Re: [PATCH v5 08/10] xen/blkback: get the number of hardware
queues/rings from blkfront
On Sat, Nov 14, 2015 at 11:12:17AM +0800, Bob Liu wrote:
> Backend advertises "multi-queue-max-queues" to front, also get the negotiated
> number from "multi-queue-num-queues" written by blkfront.
>
> Signed-off-by: Bob Liu <bob.liu@...cle.com>
> ---
> drivers/block/xen-blkback/blkback.c | 12 ++++++++++++
> drivers/block/xen-blkback/common.h | 1 +
> drivers/block/xen-blkback/xenbus.c | 34 ++++++++++++++++++++++++++++------
> 3 files changed, 41 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index fb5bfd4..acedc46 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -84,6 +84,15 @@ MODULE_PARM_DESC(max_persistent_grants,
> "Maximum number of grants to map persistently");
>
> /*
> + * Maximum number of rings/queues blkback supports, allow as many queues as there
> + * are CPUs if user has not specified a value.
> + */
> +unsigned int xenblk_max_queues;
> +module_param_named(max_queues, xenblk_max_queues, uint, 0644);
> +MODULE_PARM_DESC(max_queues,
> + "Maximum number of hardware queues per virtual disk");
Added:
unsigned int xenblk_max_queues;
module_param_named(max_queues, xenblk_max_queues, uint, 0644);
MODULE_PARM_DESC(max_queues,
- "Maximum number of hardware queues per virtual disk");
+ "Maximum number of hardware queues per virtual disk." \
+ "By default it is the number of online CPUs.");
/*
> +
> +/*
> * Maximum order of pages to be used for the shared ring between front and
> * backend, 4KB page granularity is used.
> */
> @@ -1483,6 +1492,9 @@ static int __init xen_blkif_init(void)
> xen_blkif_max_ring_order = XENBUS_MAX_RING_GRANT_ORDER;
> }
>
> + 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 f2386e3..0833dc6 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -46,6 +46,7 @@
> #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 6c6e048..d83b790 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)
> blkif->st_print = jiffies;
> 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;
> }
>
> @@ -595,6 +589,12 @@ 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");
s/num/max/
> +
> /* setup back pointer */
> be->blkif->be = be;
>
> @@ -980,6 +980,7 @@ 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);
>
> @@ -1007,6 +1008,27 @@ 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);
> + 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;
And made this return -ENOSYS.
> + }
> + }
> + be->blkif->nr_rings = requested_num_queues;
> + if (xen_blkif_alloc_rings(be->blkif))
> + return -ENOMEM;
> +
> pr_info("%s: using %d queues, protocol %d (%s) %s\n", dev->nodename,
> be->blkif->nr_rings, be->blkif->blk_protocol, protocol,
> pers_grants ? "persistent grants" : "");
> --
> 1.7.10.4
>
--
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