Module Name: src
Committed By: ad
Date: Tue May 5 22:12:07 UTC 2020
Modified Files:
src/sys/kern: sys_lwp.c
Log Message:
lwp_unpark(): no need to acquire LWP refs or drop the proc lock.
On the hacky benchmarks I have, held over from the transition to 1:1
threading, this restores pthread_cond_signal() perf to radixtree/sleepq
levels, and semes much better than either with pthread_cond_broadcast() and
10 threads. It would be interesting to see what might be achieved with a
lockless lookup, which is within grasp now thanks to pid_table being used
for lookup.
To generate a diff of this commit:
cvs rdiff -u -r1.79 -r1.80 src/sys/kern/sys_lwp.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/sys_lwp.c
diff -u src/sys/kern/sys_lwp.c:1.79 src/sys/kern/sys_lwp.c:1.80
--- src/sys/kern/sys_lwp.c:1.79 Fri Apr 24 03:22:06 2020
+++ src/sys/kern/sys_lwp.c Tue May 5 22:12:06 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: sys_lwp.c,v 1.79 2020/04/24 03:22:06 thorpej Exp $ */
+/* $NetBSD: sys_lwp.c,v 1.80 2020/05/05 22:12:06 ad Exp $ */
/*-
* Copyright (c) 2001, 2006, 2007, 2008, 2019, 2020 The NetBSD Foundation, Inc.
@@ -35,7 +35,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_lwp.c,v 1.79 2020/04/24 03:22:06 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_lwp.c,v 1.80 2020/05/05 22:12:06 ad Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@@ -467,36 +467,12 @@ lwp_unpark(const lwpid_t *tp, const u_in
mutex_enter(p->p_lock);
for (target = 0; target < ntargets; target++) {
- /*
- * We don't bother excluding idle LWPs here, as
- * setting LW_UNPARKED on them won't do any harm.
- */
t = proc_find_lwp(p, tp[target]);
if (__predict_false(t == NULL)) {
error = ESRCH;
continue;
}
- /*
- * The locking order is p::p_lock -> l::l_mutex,
- * but it may not be unsafe to release p::p_lock
- * while l::l_mutex is held because l::l_mutex is
- * a scheduler lock and we don't want to get tied
- * in knots while unwinding priority inheritance.
- * So, get a reference count on the LWP and then
- * unlock p::p_lock before acquiring l::l_mutex.
- */
- if (__predict_false(t->l_stat == LSZOMB)) {
- continue;
- }
- lwp_addref(t);
- mutex_exit(p->p_lock);
-
- /*
- * Note the LWP cannot become a zombie while we
- * hold a reference.
- */
-
lwp_lock(t);
if (__predict_true(t->l_syncobj == &lwp_park_syncobj)) {
/*
@@ -504,6 +480,9 @@ lwp_unpark(const lwpid_t *tp, const u_in
* lwp_unsleep() will release the LWP lock.
*/
lwp_unsleep(t, true);
+ } else if (__predict_false(t->l_stat == LSZOMB)) {
+ lwp_unlock(t);
+ error = ESRCH;
} else {
/*
* It hasn't parked yet because the wakeup side won
@@ -516,8 +495,6 @@ lwp_unpark(const lwpid_t *tp, const u_in
t->l_flag |= LW_UNPARKED;
lwp_unlock(t);
}
- mutex_enter(p->p_lock);
- lwp_delref2(t);
}
mutex_exit(p->p_lock);
