Date: Tue, 21 May 2002 13:47:11 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/conf NOTES options src/sys/kern kern_mutex.c Message-ID: <200205212047.g4LKlBY50788@freefall.freebsd.org>
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jhb 2002/05/21 13:47:11 PDT
Modified files:
sys/conf NOTES options
sys/kern kern_mutex.c
Log:
Add code to make default mutexes adaptive if the ADAPTIVE_MUTEXES kernel
option is used (not on by default).
- In the case of trying to lock a mutex, if the MTX_CONTESTED flag is set,
then we can safely read the thread pointer from the mtx_lock member while
holding sched_lock. We then examine the thread to see if it is currently
executing on another CPU. If it is, then we keep looping instead of
blocking.
- In the case of trying to unlock a mutex, it is now possible for a mutex
to have MTX_CONTESTED set in mtx_lock but to not have any threads
actually blocked on it, so we need to handle that case. In that case,
we just release the lock as if MTX_CONTESTED was not set and return.
- We do not adaptively spin on Giant as Giant is held for long times and
it slows SMP systems down to a crawl (it was taking several minutes,
like 5-10 or so for my test alpha and sparc64 SMP boxes to boot up when
they adaptively spinned on Giant).
- We only compile in the code to do this for SMP kernels, it doesn't make
sense for UP kernels.
Tested on: i386, alpha, sparc64
Revision Changes Path
1.1033 +5 -0 src/sys/conf/NOTES
1.318 +1 -0 src/sys/conf/options
1.92 +26 -0 src/sys/kern/kern_mutex.c
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