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Date: | Sun, 6 Dec 2015 03:34:42 +0100 |
Message-ID: | <CABPLASSY3WWpHAeh=5gqRKdg85M8Wzkrq9qMaDhzhk2zvxgcOw@mail.gmail.com> |
Subject: | Re: Cygwin multithreading performance |
From: | Kacper Michajlow <kasper93 AT gmail DOT com> |
To: | cygwin AT cygwin DOT com |
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2015-12-05 23:40 GMT+01:00 Mark Geisert <mark AT maxrnd DOT com>: > Kacper Michajlow wrote: >> >> 2015-12-05 11:51 GMT+01:00 Mark Geisert <mark AT maxrnd DOT com>: >>> >>> Mark Geisert wrote: >>> In the OP's very good testcase the most heavily contended locks, by far, >>> are >>> those internal to git's builtin/pack-objects.c. I plan to show actual >>> stats >>> after some more cleanup, but I did notice something in that git source >>> file >>> that might explain the difference between Cygwin and MinGW when running >>> this >>> testcase... >>> >>> #ifndef NO_PTHREADS >>> >>> static pthread_mutex_t read_mutex; >>> #define read_lock() pthread_mutex_lock(&read_mutex) >>> #define read_unlock() pthread_mutex_unlock(&read_mutex) >>> >>> static pthread_mutex_t cache_mutex; >>> #define cache_lock() pthread_mutex_lock(&cache_mutex) >>> #define cache_unlock() pthread_mutex_unlock(&cache_mutex) >>> >>> static pthread_mutex_t progress_mutex; >>> #define progress_lock() pthread_mutex_lock(&progress_mutex) >>> #define progress_unlock() pthread_mutex_unlock(&progress_mutex) >>> >>> #else >>> >>> #define read_lock() (void)0 >>> #define read_unlock() (void)0 >>> #define cache_lock() (void)0 >>> #define cache_unlock() (void)0 >>> #define progress_lock() (void)0 >>> #define progress_unlock() (void)0 >>> >>> #endif >>> >>> Is it possible the MinGW version of git is compiled with NO_PTHREADS >>> #defined? If so, it would mean there's no locking being done at all and >>> would explain the faster execution and near 100% CPU utilization when >>> running under MinGW. >> >> >> Nah, there is no threading enabled when there is no pthreads. How >> would that work? :D See thread-utils.h >> >> #ifndef NO_PTHREADS >> #include <pthread.h> >> >> extern int online_cpus(void); >> extern int init_recursive_mutex(pthread_mutex_t*); >> >> #else >> >> #define online_cpus() 1 >> >> #endif > > > We're not familiar at all with MinGW. Could you locate the source for > MinGW's pthread_mutex_lock() online and give us a link to it? And BTW, > which Windows are you running and on what kind of hardware (bitness and > #CPUS/threads)? > > It looks like we're going to have to compare actual pthread_mutex_lock() > implementations. Inspecting source is nice but I don't want to be chasing a > mirage so I really hope there's a pthread_mutex_lock() function inside the > MinGW git you are running. gdb could easily answer that question. Could > you please do an 'info func pthread_mutex_lock' after starting MinGW git > under MinGW gdb with a breakpoint at main() (so libraries are loaded). > > > ..mark > > > -- > 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 > Hmm, thinking about it mingw doesn't have pthread implementation or any wrapper for it. If someone needs pthread they would probably go for pthreads-w32 implementation. I started to wonder because I don't recall git would need pthreads to compile on Windows. And indeed they have a wrapper for Windows API... https://github.com/git/git/blob/master/compat/win32/pthread.h https://github.com/git/git/blob/master/compat/win32/pthread.c Though it is not really a matter that "native" git build is fast and all, but that Cygwin's one really struggles if it comes to MT workload . And this not only issue with git unfortunately. Download speeds are also limited on Cygwin. I know POSIX compatibility layers comes with a price but I would love to see improvements in those areas. Cygwin: Receiving objects: 100% (230458/230458), 78.41 MiB | 1.53 MiB/s, done. "native" git: Receiving objects: 100% (230458/230458), 78.41 MiB | 18.54 MiB/s, done. I'm on Windows 10 x64 and i7 5820K (6C/12T). -Kacper -- 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
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