b11317a643
Remove all trailing whitespace from the following list of files: *.cpp *.h *.conf *.qdoc *.pro *.pri *.mm *.rc *.pl *.qps *.xpm *.txt *README excluding 3rdparty, test-data and auto generated code. Note A): the only non 3rdparty c++-files that still have trailing whitespace after this change are: * src/corelib/codecs/cp949codetbl_p.h * src/corelib/codecs/qjpunicode.cpp * src/corelib/codecs/qbig5codec.cpp * src/corelib/xml/qxmlstream_p.h * src/tools/qdoc/qmlparser/qqmljsgrammar.cpp * src/tools/uic/ui4.cpp * tests/auto/other/qtokenautomaton/tokenizers/* * tests/benchmarks/corelib/tools/qstring/data.cpp * util/lexgen/tokenizer.cpp Note B): in about 30 files some overlapping 'leading tab' and 'TAB character in non-leading whitespace' issues have been fixed to make the sanity bot happy. Plus some general ws-fixes here and there as asked for during review. Change-Id: Ia713113c34d82442d6ce4d93d8b1cf545075d11d Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
82 lines
3.1 KiB
Plaintext
82 lines
3.1 KiB
Plaintext
The most reliable way of running benchmarks is to do it in an otherwise idle
|
|
system. On a busy system, the results will vary according to the other tasks
|
|
demanding attention in the system.
|
|
|
|
We have managed to obtain quite reliable results by doing the following on
|
|
Linux (and you need root):
|
|
|
|
- switching the scheduler to a Real-Time mode
|
|
- setting the processor affinity to one single processor
|
|
- disabling the other thread of the same core
|
|
|
|
This should work rather well for CPU-intensive tasks. A task that is in Real-
|
|
Time mode will simply not be preempted by the OS. But if you make OS syscalls,
|
|
especially I/O ones, your task will be de-scheduled. Note that this includes
|
|
page faults, so if you can, make sure your benchmark's warmup code paths touch
|
|
most of the data.
|
|
|
|
To do this you need a tool called schedtool (package schedtool), from
|
|
http://freequaos.host.sk/schedtool/
|
|
|
|
From this point on, we are using CPU0 for all tasks:
|
|
|
|
If you have a Hyperthreaded multi-core processor (Core-i5 and Core-i7), you
|
|
have to disable the other thread of the same core as CPU0. To discover which
|
|
one it is:
|
|
|
|
$ cat /sys/devices/system/cpu/cpu0/topology/thread_siblings_list
|
|
|
|
This will print something like 0,4, meaning that CPUs 0 and 4 are sibling
|
|
threads on the same core. So we'll turn CPU 4 off:
|
|
|
|
(as root)
|
|
# echo 0 > /sys/devices/system/cpu/cpu4/online
|
|
|
|
To turn it back on, echo 1 into the same file.
|
|
|
|
To run a task on CPU 0 exclusively, using FIFO RT priority 10, you run the
|
|
following:
|
|
|
|
(as root)
|
|
# schedtool -F -p 10 -a 1 -e ./taskname
|
|
|
|
For example:
|
|
# schedtool -F -p 10 -a 1 -e ./tst_bench_qstring -tickcounter
|
|
|
|
Warning: if your task livelocks or takes far too long to complete, your system
|
|
may be unusable for a long time, especially if you don't have other cores to
|
|
run stuff on. To prevent that, run it before schedtool and time it.
|
|
|
|
You can also limit the CPU time that the task is allowed to take. Run in the
|
|
same shell as you'll run schedtool:
|
|
|
|
$ ulimit -s 300
|
|
To limit to 300 seconds (5 minutes)
|
|
|
|
If your task runs away, it will get a SIGXCPU after consuming 5 minutes of CPU
|
|
time (5 minutes running at 100%).
|
|
|
|
If your app is multithreaded, you may want to give it more CPUs, like CPU0 and
|
|
CPU1 with -a 3 (it's a bitmask).
|
|
|
|
For best results, you should disable ALL other cores and threads of the same
|
|
processor. The new Core-i7 have one processor with 4 cores,
|
|
each core can run 2 threads; the older Mac Pros have two processors with 4
|
|
cores each. So on those Mac Pros, you'd disable cores 1, 2 and 3, while on the
|
|
Core-i7, you'll need to disable all other CPUs.
|
|
|
|
However, disabling just the sibling thread seems to produce very reliable
|
|
results for me already, with variance often below 0.5% (even though there are
|
|
some measurable spikes).
|
|
|
|
Other things to try:
|
|
|
|
Running the benchmark with highest priority, i.e. "sudo nice -19"
|
|
usually produces stable results on some machines. If the benchmark also
|
|
involves displaying something on the screen (on X11), running it with
|
|
"-sync" is a must. Though, in that case the "real" cost is not correct,
|
|
but it is useful to discover regressions.
|
|
|
|
Also; not many people know about ionice (1)
|
|
ionice - get/set program io scheduling class and priority
|