Re: [PATCH 1/4] cfq: Increase default value of target_latency
From: Mel Gorman <mgorman@suse.de>
Date: 2014-06-20 11:28:57
Also in:
linux-fsdevel, lkml
On Thu, Jun 19, 2014 at 02:38:44PM -0400, Jeff Moyer wrote:
Mel Gorman [off-list ref] writes:quoted
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 the default on the assumption that people with access to expensive fast storage also know how to tune their IO scheduler. The following is from tiobench run on a mid-range desktop with a single spinning disk. 3.16.0-rc1 3.16.0-rc1 3.0.0 vanilla cfq600 vanilla Mean SeqRead-MB/sec-1 121.88 ( 0.00%) 121.60 ( -0.23%) 134.59 ( 10.42%) Mean SeqRead-MB/sec-2 101.99 ( 0.00%) 102.35 ( 0.36%) 122.59 ( 20.20%) Mean SeqRead-MB/sec-4 97.42 ( 0.00%) 99.71 ( 2.35%) 114.78 ( 17.82%) Mean SeqRead-MB/sec-8 83.39 ( 0.00%) 90.39 ( 8.39%) 100.14 ( 20.09%) Mean SeqRead-MB/sec-16 68.90 ( 0.00%) 77.29 ( 12.18%) 81.64 ( 18.50%)Did you test any workloads other than this?
dd tests were inconclusive due to high variability. The dbench results hadn't come through but regression tests there indicate that it has regressed for high numbers of clients. I know sequential reads of benchmarks like bonnie++ have also regressed but I have not reverified the results yet.
Also, what normal workload has 8 or more threads doing sequential reads? (That's an honest question.)
File servers, mail servers, streaming media servers with multiple users, multi-user systems -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>