Author: mjg
Date: Wed Nov 11 08:51:04 2020
New Revision: 367585
URL: https://svnweb.freebsd.org/changeset/base/367585
Log:
thread: add more fine-grained tidhash locking
Note this still does not scale but is enough to move it out of the way
for the foreseable future.
In particular a trivial benchmark spawning/killing threads stops contesting
on tidhash.
Modified:
head/sys/kern/kern_thread.c
Modified: head/sys/kern/kern_thread.c
==============================================================================
--- head/sys/kern/kern_thread.c Wed Nov 11 08:50:04 2020 (r367584)
+++ head/sys/kern/kern_thread.c Wed Nov 11 08:51:04 2020 (r367585)
@@ -149,8 +149,10 @@ static int nthreads;
static LIST_HEAD(tidhashhead, thread) *tidhashtbl;
static u_long tidhash;
-static struct rwlock tidhash_lock;
-#define TIDHASH(tid) (&tidhashtbl[(tid) & tidhash])
+static u_long tidhashlock;
+static struct rwlock *tidhashtbl_lock;
+#define TIDHASH(tid) (&tidhashtbl[(tid) & tidhash])
+#define TIDHASHLOCK(tid) (&tidhashtbl_lock[(tid) & tidhashlock])
EVENTHANDLER_LIST_DEFINE(thread_ctor);
EVENTHANDLER_LIST_DEFINE(thread_dtor);
@@ -355,6 +357,7 @@ extern int max_threads_per_proc;
void
threadinit(void)
{
+ u_long i;
lwpid_t tid0;
uint32_t flags;
@@ -395,7 +398,13 @@ threadinit(void)
thread_ctor, thread_dtor, thread_init, thread_fini,
32 - 1, flags);
tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
- rw_init(&tidhash_lock, "tidhash");
+ tidhashlock = (tidhash + 1) / 64;
+ if (tidhashlock > 0)
+ tidhashlock--;
+ tidhashtbl_lock = malloc(sizeof(*tidhashtbl_lock) * (tidhashlock + 1),
+ M_TIDHASH, M_WAITOK | M_ZERO);
+ for (i = 0; i < tidhashlock + 1; i++)
+ rw_init(&tidhashtbl_lock[i], "tidhash");
}
/*
@@ -1351,7 +1360,7 @@ tdfind_hash(lwpid_t tid, pid_t pid, struct proc **pp,
bool locked;
run = 0;
- rw_rlock(&tidhash_lock);
+ rw_rlock(TIDHASHLOCK(tid));
locked = true;
LIST_FOREACH(td, TIDHASH(tid), td_hash) {
if (td->td_tid != tid) {
@@ -1364,11 +1373,11 @@ tdfind_hash(lwpid_t tid, pid_t pid, struct proc **pp,
break;
}
if (run > RUN_THRESH) {
- if (rw_try_upgrade(&tidhash_lock)) {
+ if (rw_try_upgrade(TIDHASHLOCK(tid))) {
LIST_REMOVE(td, td_hash);
LIST_INSERT_HEAD(TIDHASH(td->td_tid),
td, td_hash);
- rw_wunlock(&tidhash_lock);
+ rw_wunlock(TIDHASHLOCK(tid));
locked = false;
break;
}
@@ -1376,7 +1385,7 @@ tdfind_hash(lwpid_t tid, pid_t pid, struct proc **pp,
break;
}
if (locked)
- rw_runlock(&tidhash_lock);
+ rw_runlock(TIDHASHLOCK(tid));
if (td == NULL)
return (false);
*pp = p;
@@ -1421,15 +1430,16 @@ tdfind(lwpid_t tid, pid_t pid)
void
tidhash_add(struct thread *td)
{
- rw_wlock(&tidhash_lock);
+ rw_wlock(TIDHASHLOCK(td->td_tid));
LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
- rw_wunlock(&tidhash_lock);
+ rw_wunlock(TIDHASHLOCK(td->td_tid));
}
void
tidhash_remove(struct thread *td)
{
- rw_wlock(&tidhash_lock);
+
+ rw_wlock(TIDHASHLOCK(td->td_tid));
LIST_REMOVE(td, td_hash);
- rw_wunlock(&tidhash_lock);
+ rw_wunlock(TIDHASHLOCK(td->td_tid));
}
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