From: Keith Busch <keith.busch@intel.com>
To: Matthew Wilcox <willy@linux.intel.com>
Cc: Hannes Reinecke <hare@suse.de>,
lsf@lists.linux-foundation.org,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
Jens Axboe <axboe@kernel.dk>,
SCSI Mailing List <linux-scsi@vger.kernel.org>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [Lsf] [LSF/MM TOPIC] block-mq issues with FC
Date: Fri, 8 Apr 2016 18:06:21 +0000 [thread overview]
Message-ID: <20160408180621.GA6110@localhost.localdomain> (raw)
In-Reply-To: <20160408174006.GI2781@linux.intel.com>
On Fri, Apr 08, 2016 at 01:40:06PM -0400, Matthew Wilcox wrote:
> - Inability to use all queues supported by a device. Intel's P3700
> supports 31 queues, but block-mq insists on assigning an even multiple
> of CPUs to each queue. So if you have 48 CPUs, it will use 24 queues.
> If you have 128 CPUs, it will only use 16 of the queues.
While it'd be better to use all the available h/w resources, that's
actually not the worst part.
The real problems occur when there are more physical/unique CPUs than
h/w queues since blk-mq does not consider CPU topology beyond thread
siblings. With 128 CPUs, blk-mq may use all 31 queues P3700 supports,
but many CPU groups won't share a last-level-cache.
Smarter assignment would reclaim some untapped performance, and we can
share such code prior to the session.
next prev parent reply other threads:[~2016-04-08 18:06 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-08 11:29 [LSF/MM TOPIC] block-mq issues with FC Hannes Reinecke
2016-04-08 15:11 ` James Bottomley
2016-04-08 15:51 ` [Lsf] " Ewan D. Milne
2016-04-08 16:06 ` James Bottomley
2016-04-08 17:26 ` Bart Van Assche
2016-04-08 17:40 ` Matthew Wilcox
2016-04-08 18:00 ` James Bottomley
2016-04-08 18:08 ` Christoph Hellwig
2016-04-08 18:24 ` James Bottomley
2016-04-08 18:06 ` Keith Busch [this message]
2016-04-12 19:16 ` Jens Axboe
2016-04-08 18:14 ` Bart Van Assche
2016-04-08 19:22 ` Waskiewicz, PJ
2016-04-10 19:02 ` Sagi Grimberg
2016-04-12 19:04 ` Quinn Tran
2016-04-08 18:13 ` Christoph Hellwig
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