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App runs 8x slower on dual core machine (with test case to replicate issue)
- From: Zach Saw <zach dot saw at gmail dot com>
- To: cygwin at cygwin dot com
- Date: Thu, 9 Aug 2012 18:07:06 +1000
- Subject: App runs 8x slower on dual core machine (with test case to replicate issue)
While trying to compile my multithreaded app written for Linux on
Cygwin to run on Windows, I discovered the app would perform 8x slower
on a machine with the same specs. I then went on to triage the issue
and found that if I set CPU affinity of that process to 1 (i.e. single
core), I'd get it to speed up to almost the speed I'd get under Linux
(set to single core too).
I dug deeper and had my suspicion on a Cygwin bug. I suspected a
problem in its thread singalling (condvar). So to test my hypothesis,
I created a minimal test case to show case this issue. This minimal
test case compiled on MSVC++ too and the difference is staggering.
What you'll find is if you started the process with CPU Aff = 1,
you'll get it to run >8x as fast as the default.
On my machine, it took 4300ms to run in dual core mode, 460ms to run
when CPU Aff = 1.
All firewalls disabled
Virus / Malware scanners disabled
Boost 1.48.0 (as per official Cygwin installation)
[Only for test case app] Boost.Threadpool - http://threadpool.sourceforge.net
Code to replicate the issue (get Boost.Threadpool from above):
inline int GetTickCount()
return (((int)t.tv_sec) * 1000) + (t.tv_nsec / 1000000);
int main(int argc, char** argv)
start = GetTickCount();
for (int i=0; i<100000; i++)
int elapsed = GetTickCount() - start;
std::cout << elapsed << std::endl;
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