Date: Wed, 20 Feb 2002 17:02:22 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: John Baldwin <jhb@FreeBSD.org> Cc: current@FreeBSD.org Subject: Re: RE: Patch to improve mutex collision performance Message-ID: <200202210102.g1L12MR91194@apollo.backplane.com> References: <XFMail.020220172745.jhb@FreeBSD.org>
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This sounds better but why do we need a 'pause' at all? I don't
think spinning in this case will have any effect on power
consumption.
-Matt
Matthew Dillon
<dillon@backplane.com>
:I would rather make the locks adaptive like so: (untested)
:
:--- //depot/projects/smpng/sys/conf/options 2002/02/08 13:19:07
:+++ //depot/user/jhb/lock/conf/options 2002/02/08 13:50:54
:@@ -56,6 +56,7 @@
: # mapped I/O
:
: # Miscellaneous options.
:+ADAPTIVE_MUTEXES
: BLEED
: COMPAT_43 opt_compat.h
: COMPAT_SUNOS opt_compat.h
:--- //depot/projects/smpng/sys/i386/include/cpufunc.h 2001/12/18 13:07:32
:+++ //depot/user/jhb/lock/i386/include/cpufunc.h 2001/12/20 15:54:32
:@@ -550,6 +550,12 @@
: __asm __volatile("movl %0,%%dr7" : : "r" (sel));
: }
:
:+static __inline void
:+cpu_pause(void)
:+{
:+ __asm __volatile("pause");
:+}
:+
: static __inline critical_t
: cpu_critical_enter(void)
: {
:--- //depot/projects/smpng/sys/kern/kern_mutex.c 2002/02/08 14:19:21
:+++ //depot/user/jhb/lock/kern/kern_mutex.c 2002/02/08 13:50:54
:@@ -34,6 +34,7 @@
: * Machine independent bits of mutex implementation.
: */
:
:+#include "opt_adaptive_mutexes.h"
: #include "opt_ddb.h"
:
: #include <sys/param.h>
:@@ -345,7 +354,22 @@
: continue;
: }
:
:+#if defined(SMP) && defined(ADAPTIVE_MUTEXES)
: /*
:+ * If the current owner of the lock is executing on another
:+ * CPU, spin instead of blocking.
:+ */
:+ if (((struct thread *)(v & MTX_FLAGMASK)->td_kse->kse_oncpu !=
:+ NOCPU) {
:+ mtx_unlock_spin(&sched_lock);
:+#ifdef __i386__
:+ cpu_pause();
:+#endif
:+ continue;
:+ }
:+#endif /* SMP && ADAPTIVE_MUTEXES */
:+
:+ /*
: * We deffinately must sleep for this lock.
: */
: mtx_assert(m, MA_NOTOWNED);
:@@ -433,6 +457,9 @@
: /* Give interrupts a chance while we spin. */
: critical_exit();
: while (m->mtx_lock != MTX_UNOWNED) {
:+#ifdef __i386__
:+ cpu_pause();
:+#endif
: if (i++ < 10000000)
: continue;
: if (i++ < 60000000)
:
:This is more a specific problem with Giant and I don't think it will be a
:problem with other mutexes, so I'd prefer a solution not quite so tailored to
:this particular behavior of Giant.
:
:--
:
:John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
:"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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