mirror of
https://github.com/RPCS3/llvm.git
synced 2024-12-05 02:07:16 +00:00
01c176bc59
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303769 91177308-0d34-0410-b5e6-96231b3b80d8
88 lines
2.5 KiB
ReStructuredText
88 lines
2.5 KiB
ReStructuredText
==================================
|
|
Benchmarking tips
|
|
==================================
|
|
|
|
|
|
Introduction
|
|
============
|
|
|
|
For benchmarking a patch we want to reduce all possible sources of
|
|
noise as much as possible. How to do that is very OS dependent.
|
|
|
|
Note that low noise is required, but not sufficient. It does not
|
|
exclude measurement bias. See
|
|
https://www.cis.upenn.edu/~cis501/papers/producing-wrong-data.pdf for
|
|
example.
|
|
|
|
General
|
|
================================
|
|
|
|
* Use a high resolution timer, e.g. perf under linux.
|
|
|
|
* Run the benchmark multiple times to be able to recognize noise.
|
|
|
|
* Disable as many processes or services as possible on the target system.
|
|
|
|
* Disable frequency scaling, turbo boost and address space
|
|
randomization (see OS specific section).
|
|
|
|
* Static link if the OS supports it. That avoids any variation that
|
|
might be introduced by loading dynamic libraries. This can be done
|
|
by passing ``-DLLVM_BUILD_STATIC=ON`` to cmake.
|
|
|
|
* Try to avoid storage. On some systems you can use tmpfs. Putting the
|
|
program, inputs and outputs on tmpfs avoids touching a real storage
|
|
system, which can have a pretty big variability.
|
|
|
|
To mount it (on linux and freebsd at least)::
|
|
|
|
mount -t tmpfs -o size=<XX>g none dir_to_mount
|
|
|
|
Linux
|
|
=====
|
|
|
|
* Disable address space randomization::
|
|
|
|
echo 0 > /proc/sys/kernel/randomize_va_space
|
|
|
|
* Set scaling_governor to performance::
|
|
|
|
for i in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
|
|
do
|
|
echo performance > /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
|
|
done
|
|
|
|
* Use https://github.com/lpechacek/cpuset to reserve cpus for just the
|
|
program you are benchmarking. If using perf, leave at least 2 cores
|
|
so that perf runs in one and your program in another::
|
|
|
|
cset shield -c N1,N2 -k on
|
|
|
|
This will move all threads out of N1 and N2. The ``-k on`` means
|
|
that even kernel threads are moved out.
|
|
|
|
* Disable the SMT pair of the cpus you will use for the benchmark. The
|
|
pair of cpu N can be found in
|
|
``/sys/devices/system/cpu/cpuN/topology/thread_siblings_list`` and
|
|
disabled with::
|
|
|
|
echo 0 > /sys/devices/system/cpu/cpuX/online
|
|
|
|
|
|
* Run the program with::
|
|
|
|
cset shield --exec -- perf stat -r 10 <cmd>
|
|
|
|
This will run the command after ``--`` in the isolated cpus. The
|
|
particular perf command runs the ``<cmd>`` 10 times and reports
|
|
statistics.
|
|
|
|
With these in place you can expect perf variations of less than 0.1%.
|
|
|
|
Linux Intel
|
|
-----------
|
|
|
|
* Disable turbo mode::
|
|
|
|
echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo
|