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SubjectRe: [PATCH 0/1] mm: FAULT_AROUND_ORDER patchset performance data for powerpc

* Madhavan Srinivasan <maddy@linux.vnet.ibm.com> wrote:

> Performance data for different FAULT_AROUND_ORDER values from 4 socket
> Power7 system (128 Threads and 128GB memory) is below. Fault around order (FAO)
> value of 3 looks more advantageous.
>
> FAULT_AROUND_ORDER Baseline 1 3 4 5 7
>
> Linux build (make -j64)
> minor-faults 7184385 5874015 4567289 4318518 4193815 4159193
> times in seconds 61.433776136 60.865935292 59.245368038 60.630675011 60.56587624 59.828271924

Hm, I have one general observation: it's hard to tell how
(statistically) significant the time differences are, without standard
deviation numbers.

You can get stddev very easily via 'perf stat --null --repeat N'.

You can use --pre <script> and --post <script> for pre/post
measurement cleanup hooks (such as 'make clean'). So for example:

perf stat --null --repeat 3 --pre 'make defconfig; make clean >/dev/null 2>&1' make -j64 kernel/

Which run the workload 3 times and it will output something like:

9.013717158 seconds time elapsed ( +- 0.99% )

Where the +- column shows the stddev in relative percentage units.

The --null option ensures that only time measurement is done with no
overhead for the workload, no other performance metrics are taken.

The overhead of the --pre stage is not added to the measured time.

Thus you can also add really expensive steps to the --pre stage, such
as a vm_drop_caches clearing of all caches, to measure cache-cold
results.

The stddev value shows that the result is significant to about the
first fractional digit.

Thanks,

Ingo


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