Date: Tue, 03 Jan 2006 12:56:43 -0700 From: Scott Long <scottl@samsco.org> To: Daniel Eischen <deischen@freebsd.org> Cc: freebsd-hackers@freebsd.org, prime <guomingyan@gmail.com> Subject: Re: An idea of remove MUTEX_WAKE_ALL Message-ID: <43BAD6FB.9090006@samsco.org> In-Reply-To: <Pine.GSO.4.43.0601031423060.525-100000@sea.ntplx.net> References: <Pine.GSO.4.43.0601031423060.525-100000@sea.ntplx.net>
next in thread | previous in thread | raw e-mail | index | archive | help
Daniel Eischen wrote: > 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. > Adaptive mutexes are enabled by default and have been for at least a year. Scott
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?43BAD6FB.9090006>