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SubjectRe: [PATCH 1/4] cfq: Increase default value of target_latency
Date
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 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? Also, what normal workload
has 8 or more threads doing sequential reads? (That's an honest
question.)

Cheers,
Jeff


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