Date: Tue, 3 Jan 2006 14:25:57 -0500 (EST) From: Daniel Eischen <deischen@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-hackers@freebsd.org, prime <guomingyan@gmail.com> Subject: Re: An idea of remove MUTEX_WAKE_ALL Message-ID: <Pine.GSO.4.43.0601031423060.525-100000@sea.ntplx.net> In-Reply-To: <200601031252.42657.jhb@freebsd.org>
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On Tue, 3 Jan 2006, John Baldwin wrote: > On Sunday 01 January 2006 02:21 am, prime wrote: > > Hi hackers, > > I have an idea about remove the kernel option MUTEX_WAKE_ALL. > > When we unlock the mutex(in _mtx_unlock_sleep),we can directly > > give the lock to the first thread waiting on the turnstile.And a > > thread gets the mutex after he returned from turnstile_wait so he > > can simply jump out the _obtain_lock loop in _mtx_lock_sleep. > > This makes a mutex always be owned by a thread when there are threads > > waiting on the turnstile,so priority inheritance can work now. > > This idea need only a few changes in kern/kern_mutex.c .But when > > NO_ADAPTIVE_MUTEXS not set,it makes threads that spinning on other CPU > > to get the mutex have to spin for a long time,and this makes the short > > term mutex more expensive(maybe should use spin mutex instead). > > > > What do think about the idea? Thanks. > > Sun actually found that the performance was better when you did MUTEX_WAKE_ALL > because once you woke up N threads, if they don't all resume at once then > they will acquire the lock in sequence and the lock acquires and releaes will > all be simple ones rather than all being the complicated contested case. > There are more details in _Solaris Internals_. Yes, but doesn't this partly rely on having the threads spin(*) for a bit if the current lock owner is running on another CPU? Do we currently do that? (*) No, I am not referring to spin mutexes. -- DE
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