App runs 8x slower on dual core machine (with test case to replicate issue)
Zach Saw
zach.saw@gmail.com
Thu Aug 9 08:17:00 GMT 2012
Hi all,
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.
Setup:
Cygwin
WinXP SP3
2GB RAM
Core2Duo 2.33GHz
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):
#include <boost/threadpool.hpp>
#include <iostream>
#include <time.h>
inline int GetTickCount()
{
timespec t;
clock_gettime(CLOCK_MONOTONIC, &t);
return (((int)t.tv_sec) * 1000) + (t.tv_nsec / 1000000);
}
class Test
{
public:
void Add()
{
}
void Delete()
{
}
};
int main(int argc, char** argv)
{
int start;
{
boost::threadpool::pool tp(50);
Test test;
start = GetTickCount();
for (int i=0; i<100000; i++)
{
tp.schedule(boost::bind(&Test::Add, &test));
tp.schedule(boost::bind(&Test::Delete, &test));
}
tp.wait();
}
int elapsed = GetTickCount() - start;
std::cout << elapsed << std::endl;
std::cin.get();
return 0;
}
Cheers,
Zach
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
More information about the Cygwin
mailing list