From: Kacper Michajlow <kasper93@gmail.com>
To: cygwin@cygwin.com
Subject: Re: Cygwin multithreading performance
Date: Sun, 06 Dec 2015 02:35:00 -0000 [thread overview]
Message-ID: <CABPLASSY3WWpHAeh=5gqRKdg85M8Wzkrq9qMaDhzhk2zvxgcOw@mail.gmail.com> (raw)
In-Reply-To: <566367C8.5020703@maxrnd.com>
2015-12-05 23:40 GMT+01:00 Mark Geisert <mark@maxrnd.com>:
> Kacper Michajlow wrote:
>>
>> 2015-12-05 11:51 GMT+01:00 Mark Geisert <mark@maxrnd.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/
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>
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
--
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next prev parent reply other threads:[~2015-12-06 2:35 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-14 0:24 Kacper Michajlow
2015-11-19 20:24 ` Mark Geisert
2015-11-20 14:25 ` Kacper Michajlow
2015-11-21 9:21 ` Mark Geisert
2015-11-21 10:53 ` Corinna Vinschen
2015-11-23 7:45 ` Mark Geisert
2015-11-23 10:27 ` John Hein
2015-11-24 1:05 ` Mark Geisert
2015-11-26 9:49 ` Corinna Vinschen
2015-11-26 10:49 ` Mark Geisert
2015-12-05 10:51 ` Mark Geisert
2015-12-05 13:07 ` Kacper Michajlow
2015-12-05 13:59 ` Kacper Michajlow
2015-12-05 22:40 ` Mark Geisert
2015-12-06 2:35 ` Kacper Michajlow [this message]
2015-12-06 8:02 ` Mark Geisert
2015-12-06 20:56 ` Kacper Michajlow
2015-12-08 10:51 ` Mark Geisert
2015-12-08 15:34 ` Corinna Vinschen
2015-12-08 17:02 ` Corinna Vinschen
2015-12-18 15:06 ` Achim Gratz
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