Author: mjg Date: Wed Jul 22 12:30:31 2020 New Revision: 363415 URL: https://svnweb.freebsd.org/changeset/base/363415
Log: lockmgr: add adaptive spinning 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 Modified: head/sys/kern/kern_lock.c head/sys/sys/lockmgr.h head/sys/ufs/ffs/ffs_vnops.c Modified: head/sys/kern/kern_lock.c ============================================================================== --- head/sys/kern/kern_lock.c Wed Jul 22 10:00:13 2020 (r363414) +++ head/sys/kern/kern_lock.c Wed Jul 22 12:30:31 2020 (r363415) @@ -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 * 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, struc uint64_t waittime = 0; int contested = 0; #endif + struct lock_delay_arg lda; if (KERNEL_PANICKED()) goto out; @@ -566,9 +604,31 @@ lockmgr_slock_hard(struct lock *lk, u_int flags, struc 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 @@ -576,18 +636,6 @@ lockmgr_slock_hard(struct lock *lk, u_int flags, struc &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, struc 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, struc 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, struc 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 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 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 Modified: head/sys/sys/lockmgr.h ============================================================================== --- head/sys/sys/lockmgr.h Wed Jul 22 10:00:13 2020 (r363414) +++ head/sys/sys/lockmgr.h Wed Jul 22 12:30:31 2020 (r363415) @@ -170,6 +170,7 @@ _lockmgr_args_rw(struct lock *lk, u_int flags, struct #define LK_SLEEPFAIL 0x000800 #define LK_TIMELOCK 0x001000 #define LK_NODDLKTREAT 0x002000 +#define LK_ADAPTIVE 0x004000 /* * Operations for lockmgr(). Modified: head/sys/ufs/ffs/ffs_vnops.c ============================================================================== --- head/sys/ufs/ffs/ffs_vnops.c Wed Jul 22 10:00:13 2020 (r363414) +++ head/sys/ufs/ffs/ffs_vnops.c Wed Jul 22 12:30:31 2020 (r363415) @@ -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 } _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
