From: Jeff Moyer <jmoyer@redhat.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Linux-FSDevel <linux-fsdevel@vger.kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Jens Axboe <axboe@kernel.dk>, Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH 6/6] cfq: Increase default value of target_latency
Date: Thu, 26 Jun 2014 11:36:50 -0400 [thread overview]
Message-ID: <x491tub65t9.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <1403683129-10814-7-git-send-email-mgorman@suse.de> (Mel Gorman's message of "Wed, 25 Jun 2014 08:58:49 +0100")
Mel Gorman <mgorman@suse.de> writes:
> The existing CFQ default target_latency results in very poor performance
> for larger numbers of threads doing sequential reads. While this can be
> easily described as a tuning problem for users, it is one that is tricky
> to detect. This patch updates the default to benefit smaller machines.
> Dave Chinner points out that it is dangerous to assume that people know
> how to tune their IO scheduler. Jeff Moyer asked what workloads even
> care about threaded readers but it's reasonable to assume file,
> media, database and multi-user servers all experience large sequential
> readers from multiple sources at the same time.
Right, and I guess I hadn't considered that case as I thought folks used
more than one spinning disk for such workloads.
My main reservation about this change is that you've only provided
numbers for one benchmark. To bump the default target_latency, ideally
we'd know how it affects other workloads. However, I'm having a hard
time justifying putting any time into this for a couple of reasons:
1) blk-mq pretty much does away with the i/o scheduler, and that is the
future
2) there is work in progress to convert cfq into bfq, and that will
essentially make any effort put into this irrelevant (so it might be
interesting to test your workload with bfq)
Cheers,
Jeff
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next prev parent reply other threads:[~2014-06-26 15:36 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-25 7:58 [PATCH 0/6] Improve sequential read throughput v2 Mel Gorman
2014-06-25 7:58 ` [PATCH 1/6] mm: pagemap: Avoid unnecessary overhead when tracepoints are deactivated Mel Gorman
2014-06-25 7:58 ` [PATCH 2/6] mm: Rearrange zone fields into read-only, page alloc, statistics and page reclaim lines Mel Gorman
2014-06-25 7:58 ` [PATCH 3/6] mm: vmscan: Do not reclaim from lower zones if they are balanced Mel Gorman
2014-06-25 23:32 ` Andrew Morton
2014-06-26 10:17 ` Mel Gorman
2014-06-25 7:58 ` [PATCH 4/6] mm: page_alloc: Reduce cost of the fair zone allocation policy Mel Gorman
2014-06-25 7:58 ` [PATCH 5/6] mm: page_alloc: Reduce cost of dirty zone balancing Mel Gorman
2014-06-25 23:35 ` Andrew Morton
2014-06-26 8:43 ` Mel Gorman
2014-06-26 14:37 ` Johannes Weiner
2014-06-26 14:56 ` Mel Gorman
2014-06-26 15:11 ` Johannes Weiner
2014-06-25 7:58 ` [PATCH 6/6] cfq: Increase default value of target_latency Mel Gorman
2014-06-26 15:36 ` Jeff Moyer [this message]
2014-06-26 16:19 ` Mel Gorman
2014-06-26 16:50 ` Jeff Moyer
2014-06-26 17:45 ` Mel Gorman
2014-06-26 18:04 ` Jeff Moyer
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