Fix some bugs related to adaptive spinning:
In the lockmgr support: - GIANT_RESTORE() is just called when the sleep finishes, so the current code can ends up into a giant unlock problem. Fix it by appropriately call GIANT_RESTORE() when needed. Note that this is not exactly ideal because for any interation of the adaptive spinning we drop and restore Giant, but the overhead should be not a factor. - In the lock held in exclusive mode case, after the adaptive spinning is brought to completition, we should just retry to acquire the lock instead to fallthrough. Fix that. - Fix a style nit In the sx support: - Call GIANT_SAVE() before than looping. This saves some overhead because in the current code GIANT_SAVE() is called several times. Tested by: Giovanni Trematerra <giovanni dot trematerra at gmail dot com>
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parent
c8e648e167
commit
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=196772
@ -467,7 +467,10 @@ __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
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/*
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* If the owner is running on another CPU, spin until
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* the owner stops running or the state of the lock
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* changes.
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* changes. We need a double-state handle here
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* because for a failed acquisition the lock can be
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* either held in exclusive mode or shared mode
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* (for the writer starvation avoidance technique).
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*/
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if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 &&
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LK_HOLDER(x) != LK_KERNPROC) {
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@ -491,8 +494,10 @@ __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
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while (LK_HOLDER(lk->lk_lock) ==
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(uintptr_t)owner && TD_IS_RUNNING(owner))
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cpu_spinwait();
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GIANT_RESTORE();
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continue;
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} else if (LK_CAN_ADAPT(lk, flags) &&
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(x & LK_SHARE) !=0 && LK_SHARERS(x) &&
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(x & LK_SHARE) != 0 && LK_SHARERS(x) &&
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spintries < alk_retries) {
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if (flags & LK_INTERLOCK) {
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class->lc_unlock(ilk);
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@ -511,6 +516,7 @@ __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
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break;
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cpu_spinwait();
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}
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GIANT_RESTORE();
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if (i != alk_loops)
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continue;
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}
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@ -704,6 +710,8 @@ __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
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while (LK_HOLDER(lk->lk_lock) ==
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(uintptr_t)owner && TD_IS_RUNNING(owner))
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cpu_spinwait();
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GIANT_RESTORE();
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continue;
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} else if (LK_CAN_ADAPT(lk, flags) &&
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(x & LK_SHARE) != 0 && LK_SHARERS(x) &&
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spintries < alk_retries) {
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@ -727,6 +735,7 @@ __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
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break;
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cpu_spinwait();
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}
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GIANT_RESTORE();
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if (i != alk_loops)
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continue;
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}
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@ -531,13 +531,13 @@ _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
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continue;
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}
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} else if (SX_SHARERS(x) && spintries < asx_retries) {
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GIANT_SAVE();
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spintries++;
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for (i = 0; i < asx_loops; i++) {
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if (LOCK_LOG_TEST(&sx->lock_object, 0))
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CTR4(KTR_LOCK,
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"%s: shared spinning on %p with %u and %u",
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__func__, sx, spintries, i);
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GIANT_SAVE();
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x = sx->sx_lock;
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if ((x & SX_LOCK_SHARED) == 0 ||
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SX_SHARERS(x) == 0)
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