From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752754AbbJEPPR (ORCPT ); Mon, 5 Oct 2015 11:15:17 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:3599 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750979AbbJEPPP (ORCPT ); Mon, 5 Oct 2015 11:15:15 -0400 X-IronPort-AV: E=Sophos;i="5.17,639,1437436800"; d="scan'208";a="308154606" Subject: Re: [PATCH v3 9/9] xen/blkback: get number of hardware queues/rings from blkfront To: Bob Liu , References: <1441456782-31318-1-git-send-email-bob.liu@oracle.com> <1441456782-31318-10-git-send-email-bob.liu@oracle.com> CC: , , , , , , , , , From: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= X-Enigmail-Draft-Status: N1110 Message-ID: <561293F9.1050006@citrix.com> Date: Mon, 5 Oct 2015 17:15:05 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <1441456782-31318-10-git-send-email-bob.liu@oracle.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org El 05/09/15 a les 14.39, Bob Liu ha escrit: > Backend advertises "multi-queue-max-queues" to front, and then read back the > final negotiated queues/rings from "multi-queue-num-queues" which is wrote by > blkfront. > > Signed-off-by: Bob Liu > --- > drivers/block/xen-blkback/blkback.c | 8 ++++++++ > drivers/block/xen-blkback/xenbus.c | 36 ++++++++++++++++++++++++++++++----- > 2 files changed, 39 insertions(+), 5 deletions(-) > > diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c > index fd02240..b904fe05f0 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; > +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. > @@ -1458,6 +1463,9 @@ 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, by default */ > + xenblk_max_queues = num_online_cpus(); Hm, I'm not sure of the best way to set a default value for this. Consider for example a scenario were Dom0 is limited to 2vCPUs, but DomU has 8 vCPUs. Are we going to limit the number of queues to two? Is that the most appropriate value from a performance PoV? I have to admit I don't have a clear idea of a default value for this field, and maybe the number of CPUs on the backend is indeed what works better, but there needs to be a comment explaining the reasoning behind this setting. > rc = xen_blkif_interface_init(); > if (rc) > goto failed_init; > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c > index 04b8d0d..aa97ea5 100644 > --- a/drivers/block/xen-blkback/xenbus.c > +++ b/drivers/block/xen-blkback/xenbus.c > @@ -28,6 +28,8 @@ > #define RINGREF_NAME_LEN (20) > #define RINGREF_NAME_LEN (20) > > +extern unsigned int xenblk_max_queues; This should live in blkback/common.h > + > struct backend_info { > struct xenbus_device *dev; > struct xen_blkif *blkif; > @@ -191,11 +193,6 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid) > atomic_set(&blkif->drain, 0); > INIT_WORK(&blkif->free_work, xen_blkif_deferred_free); > > - blkif->nr_rings = 1; > - if (xen_blkif_alloc_rings(blkif)) { > - kmem_cache_free(xen_blkif_cachep, blkif); > - return ERR_PTR(-ENOMEM); > - } > return blkif; > } > > @@ -618,6 +615,14 @@ static int xen_blkbk_probe(struct xenbus_device *dev, > goto fail; > } > > + /* Multi-queue: wrte how many queues backend supported. */ ^ 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_debug("Error writing multi-queue-num-queues\n"); ^ pr_warn at least. > + goto fail; > + } > + > /* setup back pointer */ > be->blkif->be = be; > > @@ -1008,6 +1013,7 @@ 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); > > @@ -1035,6 +1041,26 @@ 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 queus from frontend. ^ queues > + */ > + 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; > + } > + } > + 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" : ""); >