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lockmgr: add adaptive spinning

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It is very conservative. Only spinning when LK_ADAPTIVE is passed, only on
exclusive lock and never when any waiters are present. buffer cache is remains
not spinning.

This reduces total sleep times during buildworld etc., but it does not shorten
total real time (culprits are contention in the vm subsystem along with slock +
upgrade which is not covered).

For microbenchmarks: open3_processes -t 52 (open/close of the same file for
writing) ops/s:
before: 258845
after: 801638

Reviewed by:	kib
Tested by:	pho
Differential Revision:	https://reviews.freebsd.org/D25753
This commit is contained in:
Mateusz Guzik 2020-07-22 12:30:31 +00:00
parent fcf69f3dbc
commit 31ad4050fe
3 changed files with 114 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

129
sys/kern/kern_lock.c
View File

@ -167,6 +167,12 @@ struct lock_class lock_class_lockmgr = {
#endif
};
static __read_mostly bool lk_adaptive = true;
static SYSCTL_NODE(_debug, OID_AUTO, lockmgr, CTLFLAG_RD, NULL, "lockmgr debugging");
SYSCTL_BOOL(_debug_lockmgr, OID_AUTO, adaptive_spinning, CTLFLAG_RW, &lk_adaptive,
0, "");
#define lockmgr_delay locks_delay
struct lockmgr_wait {
const char *iwmesg;
int ipri;
@ -515,7 +521,6 @@ lockmgr_slock_try(struct lock *lk, uintptr_t *xp, int flags, bool fp)
* waiters, if we fail to acquire the shared lock
* loop back and retry.
*/
*xp = lockmgr_read_value(lk);
while (LK_CAN_SHARE(*xp, flags, fp)) {
if (atomic_fcmpset_acq_ptr(&lk->lk_lock, xp,
*xp + LK_ONE_SHARER)) {
@ -541,6 +546,38 @@ lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp)
return (false);
}
static bool
lockmgr_slock_adaptive(struct lock_delay_arg *lda, struct lock *lk, uintptr_t *xp,
int flags)
{
struct thread *owner;
uintptr_t x;
x = *xp;
MPASS(x != LK_UNLOCKED);
owner = (struct thread *)LK_HOLDER(x);
for (;;) {
MPASS(owner != curthread);
if (owner == (struct thread *)LK_KERNPROC)
return (false);
if ((x & LK_SHARE) && LK_SHARERS(x) > 0)
return (false);
if (owner == NULL)
return (false);
if (!TD_IS_RUNNING(owner))
return (false);
if ((x & LK_ALL_WAITERS) != 0)
return (false);
lock_delay(lda);
x = lockmgr_read_value(lk);
if (LK_CAN_SHARE(x, flags, false)) {
*xp = x;
return (true);
}
owner = (struct thread *)LK_HOLDER(x);
}
}
static __noinline int
lockmgr_slock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *file, int line, struct lockmgr_wait *lwa)
@ -557,6 +594,7 @@ lockmgr_slock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
uint64_t waittime = 0;
int contested = 0;
#endif
struct lock_delay_arg lda;
if (KERNEL_PANICKED())
goto out;
@ -566,27 +604,37 @@ lockmgr_slock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
file, line, flags & LK_INTERLOCK ? ilk : NULL);
lock_delay_arg_init(&lda, &lockmgr_delay);
if (!lk_adaptive)
flags &= ~LK_ADAPTIVE;
x = lockmgr_read_value(lk);
/*
* The lock may already be locked exclusive by curthread,
* avoid deadlock.
*/
if (LK_HOLDER(x) == tid) {
LOCK_LOG2(lk,
"%s: %p already held in exclusive mode",
__func__, lk);
error = EDEADLK;
goto out;
}
for (;;) {
if (lockmgr_slock_try(lk, &x, flags, false))
break;
if ((flags & (LK_ADAPTIVE | LK_INTERLOCK)) == LK_ADAPTIVE) {
if (lockmgr_slock_adaptive(&lda, lk, &x, flags))
continue;
}
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&lk->lock_object,
&contested, &waittime);
/*
* If the lock is already held by curthread in
* exclusive way avoid a deadlock.
*/
if (LK_HOLDER(x) == tid) {
LOCK_LOG2(lk,
"%s: %p already held in exclusive mode",
__func__, lk);
error = EDEADLK;
break;
}
/*
* If the lock is expected to not sleep just give up
* and return.
@ -660,6 +708,7 @@ retry_sleepq:
}
LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
__func__, lk);
x = lockmgr_read_value(lk);
}
if (error == 0) {
#ifdef KDTRACE_HOOKS
@ -682,6 +731,37 @@ out:
return (error);
}
static bool
lockmgr_xlock_adaptive(struct lock_delay_arg *lda, struct lock *lk, uintptr_t *xp)
{
struct thread *owner;
uintptr_t x;
x = *xp;
MPASS(x != LK_UNLOCKED);
owner = (struct thread *)LK_HOLDER(x);
for (;;) {
MPASS(owner != curthread);
if (owner == NULL)
return (false);
if ((x & LK_SHARE) && LK_SHARERS(x) > 0)
return (false);
if (owner == (struct thread *)LK_KERNPROC)
return (false);
if (!TD_IS_RUNNING(owner))
return (false);
if ((x & LK_ALL_WAITERS) != 0)
return (false);
lock_delay(lda);
x = lockmgr_read_value(lk);
if (x == LK_UNLOCKED) {
*xp = x;
return (true);
}
owner = (struct thread *)LK_HOLDER(x);
}
}
static __noinline int
lockmgr_xlock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *file, int line, struct lockmgr_wait *lwa)
@ -699,6 +779,7 @@ lockmgr_xlock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
uint64_t waittime = 0;
int contested = 0;
#endif
struct lock_delay_arg lda;
if (KERNEL_PANICKED())
goto out;
@ -747,10 +828,19 @@ lockmgr_xlock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
goto out;
}
x = LK_UNLOCKED;
lock_delay_arg_init(&lda, &lockmgr_delay);
if (!lk_adaptive)
flags &= ~LK_ADAPTIVE;
for (;;) {
if (lk->lk_lock == LK_UNLOCKED &&
atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid))
break;
if (x == LK_UNLOCKED) {
if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x, tid))
break;
}
if ((flags & (LK_ADAPTIVE | LK_INTERLOCK)) == LK_ADAPTIVE) {
if (lockmgr_xlock_adaptive(&lda, lk, &x))
continue;
}
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
@ -853,6 +943,7 @@ retry_sleepq:
}
LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
__func__, lk);
x = lockmgr_read_value(lk);
}
if (error == 0) {
#ifdef KDTRACE_HOOKS
@ -954,6 +1045,7 @@ lockmgr_lock_flags(struct lock *lk, u_int flags, struct lock_object *ilk,
file, line, flags & LK_INTERLOCK ? ilk : NULL);
if (__predict_false(lk->lock_object.lo_flags & LK_NOSHARE))
break;
x = lockmgr_read_value(lk);
if (lockmgr_slock_try(lk, &x, flags, true)) {
lockmgr_note_shared_acquire(lk, 0, 0,
file, line, flags);
@ -1139,12 +1231,13 @@ lockmgr_slock(struct lock *lk, u_int flags, const char *file, int line)
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
file, line, NULL);
x = lockmgr_read_value(lk);
if (__predict_true(lockmgr_slock_try(lk, &x, flags, true))) {
lockmgr_note_shared_acquire(lk, 0, 0, file, line, flags);
return (0);
}
return (lockmgr_slock_hard(lk, flags, NULL, file, line, NULL));
return (lockmgr_slock_hard(lk, flags | LK_ADAPTIVE, NULL, file, line, NULL));
}
int
@ -1165,7 +1258,7 @@ lockmgr_xlock(struct lock *lk, u_int flags, const char *file, int line)
return (0);
}
return (lockmgr_xlock_hard(lk, flags, NULL, file, line, NULL));
return (lockmgr_xlock_hard(lk, flags | LK_ADAPTIVE, NULL, file, line, NULL));
}
int

1
sys/sys/lockmgr.h
View File

@ -170,6 +170,7 @@ _lockmgr_args_rw(struct lock *lk, u_int flags, struct rwlock *ilk,
#define LK_SLEEPFAIL 0x000800
#define LK_TIMELOCK 0x001000
#define LK_NODDLKTREAT 0x002000
#define LK_ADAPTIVE 0x004000
/*
* Operations for lockmgr().

2
sys/ufs/ffs/ffs_vnops.c
View File

@ -445,6 +445,7 @@ ffs_lock(ap)
struct lock *lkp;
int result;
ap->a_flags |= LK_ADAPTIVE;
switch (ap->a_flags & LK_TYPE_MASK) {
case LK_SHARED:
case LK_UPGRADE:
@ -482,6 +483,7 @@ ffs_lock(ap)
}
return (result);
#else
ap->a_flags |= LK_ADAPTIVE;
return (VOP_LOCK1_APV(&ufs_vnodeops, ap));
#endif
}