2015-12-06 9:02 GMT+01:00 Mark Geisert <m...@maxrnd.com>: > Kacper Michajlow wrote: >> >> 2015-12-05 23:40 GMT+01:00 Mark Geisert <m...@maxrnd.com>: >>> >>> 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). > > [...] >> >> 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 > > > OK, so git has its own pthread_mutex_lock/unlock ops which map to very > light-weight critical section operations. > >> 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. > > > In the worst cases I see using your testcase, about half the time the > busiest locks are processed within 1 usec but there's a spectrum of longer > latencies for the other half of the time. I don't know (yet) if that can be > improved in Cygwin's more general implementation but at least the matter has > now been brought to our attention :). , Yes, I can imagine, git's objects are very small so threading overhead is very noticeable.
>> 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. > > > You're asserting this additional testcase has the same cause. What is > telling you that? And FTR what is the git command you are issuing? I can > then do the lock latency analysis on this new testcase if warranted. No, sorry, I mixed different things. It is just that I'm ruining both git build lately and I wanted to share another issue before I forget about it. This was git clone command for some random repository from github. There is a lot factors at hand here but the fact is with cygwin speed is capped on 1.5MB/s and this is reproducible. This is probably also related to the fact that git operates on large amount small object. But this time it is single thread workload. I tried strace this, but frankly I am not sure what to look for. All in all I just want to bring those issues to your attention. Whether it is fixable or not is another story. But we will not know unless someone with required knowledge analyze it. -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
