* Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx> 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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