Date: Tue, 30 Oct 2007 09:55:35 +0800 From: David Xu <davidxu@FreeBSD.org> To: Kris Kennaway <kris@FreeBSD.org> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/lib/libthr/thread thr_mutex.c src/lib/libkse/thread thr_mutex.c src/include pthread.h Message-ID: <47268F17.1000106@freebsd.org> In-Reply-To: <200710292101.l9TL1mAE049561@repoman.freebsd.org> References: <200710292101.l9TL1mAE049561@repoman.freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
Kris Kennaway wrote: > kris 2007-10-29 21:01:47 UTC > > FreeBSD src repository > > Modified files: > lib/libthr/thread thr_mutex.c > lib/libkse/thread thr_mutex.c > include pthread.h > Log: > Add a new "non-portable" mutex type, PTHREAD_MUTEX_ADAPTIVE_NP. This > is also implemented in glibc and is used by a number of existing > applications (mysql, firefox, etc). > > This mutex type is a default mutex with the additional property that > it spins briefly when attempting to acquire a contested lock, doing > trylock operations in userland before entering the kernel to block if > eventually unsuccessful. > > The expectation is that applications requesting this mutex type know > that the mutex is likely to be only held for very brief periods, so it > is faster to spin in userland and probably succeed in acquiring the > mutex, than to enter the kernel and sleep, only to be woken up almost > immediately. This can help significantly in certain cases when > pthread mutexes are heavily contended and held for brief durations > (such as mysql). > > Spin up to 200 times before entering the kernel, which represents only > a few us on modern CPUs. No performance degradation was observed with > this value and it is sufficient to avoid a large performance drop in > mysql performance in the heavily contended pthread mutex case. > > The libkse implementation is a NOP. > > Reviewed by: jeff > MFC after: 3 days > > Revision Changes Path > 1.41 +2 -0 src/include/pthread.h > 1.54 +3 -0 src/lib/libkse/thread/thr_mutex.c > 1.55 +29 -0 src/lib/libthr/thread/thr_mutex.c > I am not sure PTHREAD_MUTEX_ADAPTIVE_NP is a correct solution, in fact I think this is Linux crap, shouldn't PTHREAD_PRIO_PROTECT and PTHREAD_PRIO_INHERIT mutex be adaptivly spinned ? also this commit does not change mutex_self_lock() to handle the PTHREAD_MUTEX_ADAPTIVE_NP, what is the PTHREAD_MUTEX_ADAPTIVE_NP definition when the mutex is already locked by the currect thread ? deadlock or return error code ? The spinning loop is also sub-optimized, it runs every spin loop with bus lock instruction. Regards, David Xu
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?47268F17.1000106>