Author: mjg
Date: Mon Feb 19 00:38:14 2018
New Revision: 329540
URL: https://svnweb.freebsd.org/changeset/base/329540
Log:
mtx: add mtx_spin_wait_unlocked
The primitive can be used to wait for the lock to be released. Intended
usage is for locks in structures which are about to be freed.
The benefit is the avoided interrupt enable/disable trip + atomic op to
grab the lock and shorter wait if the lock is held (since there is no
worry someone will contend on the lock, re-reads can be more aggressive).
Briefly discussed with: kib
Modified:
head/sys/kern/kern_mutex.c
head/sys/sys/mutex.h
Modified: head/sys/kern/kern_mutex.c
==============================================================================
--- head/sys/kern/kern_mutex.c Sun Feb 18 23:35:23 2018 (r329539)
+++ head/sys/kern/kern_mutex.c Mon Feb 19 00:38:14 2018 (r329540)
@@ -1226,6 +1226,23 @@ _mtx_lock_indefinite_check(struct mtx *m, struct lock_
cpu_spinwait();
}
+void
+mtx_spin_wait_unlocked(struct mtx *m)
+{
+ struct lock_delay_arg lda;
+
+ lda.spin_cnt = 0;
+
+ while (atomic_load_acq_ptr(&m->mtx_lock) != MTX_UNOWNED) {
+ if (__predict_true(lda.spin_cnt < 10000000)) {
+ cpu_spinwait();
+ lda.spin_cnt++;
+ } else {
+ _mtx_lock_indefinite_check(m, &lda);
+ }
+ }
+}
+
#ifdef DDB
void
db_show_mtx(const struct lock_object *lock)
Modified: head/sys/sys/mutex.h
==============================================================================
--- head/sys/sys/mutex.h Sun Feb 18 23:35:23 2018 (r329539)
+++ head/sys/sys/mutex.h Mon Feb 19 00:38:14 2018 (r329540)
@@ -125,6 +125,8 @@ int __mtx_trylock_spin_flags(volatile uintptr_t *c, in
const char *file, int line);
void __mtx_unlock_spin_flags(volatile uintptr_t *c, int opts,
const char *file, int line);
+void mtx_spin_wait_unlocked(struct mtx *m);
+
#if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
void __mtx_assert(const volatile uintptr_t *c, int what, const char *file,
int line);
_______________________________________________
svn-src-head@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/svn-src-head
To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
