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
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