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Add code to make default mutexes adaptive if the ADAPTIVE_MUTEXES kernel

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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
This commit is contained in:
John Baldwin 2002-05-21 20:47:11 +00:00
parent a05068c0d6
commit 2498cf8c42
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=97081
4 changed files with 58 additions and 0 deletions
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5
sys/conf/NOTES
View File

@ -120,6 +120,11 @@ options ROOTDEVNAME=\"ufs:da0s2e\"
# Mandatory:
options SMP # Symmetric MultiProcessor Kernel
# ADAPTIVE_MUTEXES changes the behavior of blocking mutexes to spin
# if the thread that currently owns the mutex is executing on another
# CPU.
options ADAPTIVE_MUTEXES
# SMP Debugging Options:
#
# MUTEX_DEBUG enables various extra assertions in the mutex code.

1
sys/conf/options
View File

@ -57,6 +57,7 @@ ADW_ALLOW_MEMIO opt_adw.h # Allow PCI devices to use memory
# Miscellaneous options.
GEOM opt_geom.h
ADAPTIVE_MUTEXES
COMPAT_43 opt_compat.h
COMPAT_SUNOS opt_compat.h
COMPILING_LINT opt_global.h

26
sys/kern/kern_mutex.c
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@ -34,6 +34,7 @@
* Machine independent bits of mutex implementation.
*/
#include "opt_adaptive_mutexes.h"
#include "opt_ddb.h"
#include <sys/param.h>
@ -459,6 +460,9 @@ void
_mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
{
struct thread *td = curthread;
#if defined(SMP) && defined(ADAPTIVE_MUTEXES)
struct thread *owner;
#endif
if ((m->mtx_lock & MTX_FLAGMASK) == (uintptr_t)td) {
m->mtx_recurse++;
@ -514,6 +518,19 @@ _mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
continue;
}
#if defined(SMP) && defined(ADAPTIVE_MUTEXES)
/*
* If the current owner of the lock is executing on another
* CPU, spin instead of blocking.
*/
owner = (struct thread *)(v & MTX_FLAGMASK);
if (m != &Giant && owner->td_kse != NULL &&
owner->td_kse->ke_oncpu != NOCPU) {
mtx_unlock_spin(&sched_lock);
continue;
}
#endif /* SMP && ADAPTIVE_MUTEXES */
/*
* We definitely must sleep for this lock.
*/
@ -651,6 +668,15 @@ _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
td1 = TAILQ_FIRST(&m->mtx_blocked);
#if defined(SMP) && defined(ADAPTIVE_MUTEXES)
if (td1 == NULL) {
_release_lock_quick(m);
if (LOCK_LOG_TEST(&m->mtx_object, opts))
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p no sleepers", m);
mtx_unlock_spin(&sched_lock);
return;
}
#endif
MPASS(td->td_proc->p_magic == P_MAGIC);
MPASS(td1->td_proc->p_magic == P_MAGIC);

26
sys/kern/subr_turnstile.c
View File

@ -34,6 +34,7 @@
* Machine independent bits of mutex implementation.
*/
#include "opt_adaptive_mutexes.h"
#include "opt_ddb.h"
#include <sys/param.h>
@ -459,6 +460,9 @@ void
_mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
{
struct thread *td = curthread;
#if defined(SMP) && defined(ADAPTIVE_MUTEXES)
struct thread *owner;
#endif
if ((m->mtx_lock & MTX_FLAGMASK) == (uintptr_t)td) {
m->mtx_recurse++;
@ -514,6 +518,19 @@ _mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
continue;
}
#if defined(SMP) && defined(ADAPTIVE_MUTEXES)
/*
* If the current owner of the lock is executing on another
* CPU, spin instead of blocking.
*/
owner = (struct thread *)(v & MTX_FLAGMASK);
if (m != &Giant && owner->td_kse != NULL &&
owner->td_kse->ke_oncpu != NOCPU) {
mtx_unlock_spin(&sched_lock);
continue;
}
#endif /* SMP && ADAPTIVE_MUTEXES */
/*
* We definitely must sleep for this lock.
*/
@ -651,6 +668,15 @@ _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
td1 = TAILQ_FIRST(&m->mtx_blocked);
#if defined(SMP) && defined(ADAPTIVE_MUTEXES)
if (td1 == NULL) {
_release_lock_quick(m);
if (LOCK_LOG_TEST(&m->mtx_object, opts))
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p no sleepers", m);
mtx_unlock_spin(&sched_lock);
return;
}
#endif
MPASS(td->td_proc->p_magic == P_MAGIC);
MPASS(td1->td_proc->p_magic == P_MAGIC);