On Tue, Oct 10, 2023 at 05:26:14PM +0300, Vitaliy Makkoveev wrote:
> On Tue, Oct 10, 2023 at 09:06:23AM -0500, Scott Cheloha wrote:
> > On Fri, Oct 06, 2023 at 03:41:39PM +0200, Alexander Bluhm wrote:
> > > On Fri, Oct 06, 2023 at 03:47:31PM +0300, Vitaliy Makkoveev wrote:
> > > > On Fri, Oct 06, 2023 at 02:14:52PM +0200, Alexander Bluhm wrote:
> > > > > > @@ -718,11 +743,13 @@ softclock(void *arg)
> > > > > > softclock_process_tick_timeout(to, new);
> > > > > > }
> > > > > > tostat.tos_softclocks++;
> > > > > > - needsproc = !CIRCQ_EMPTY(&timeout_proc);
> > > > > > - mtx_leave(&timeout_mutex);
> > > > > > -
> > > > > > - if (needsproc)
> > > > > > + if (!CIRCQ_EMPTY(&timeout_proc))
> > > > > > wakeup(&timeout_proc);
> > > > > > +#ifdef MULTIPROCESSOR
> > > > > > + if(!CIRCQ_EMPTY(&timeout_proc_mpsafe))
> > > > > > + wakeup(&timeout_proc_mpsafe);
> > > > > > +#endif
> > > > > > + mtx_leave(&timeout_mutex);
> > > > > > }
> > > > > >
> > > > > > void
> > > > >
> > > > > Was there a good reason that wakeup() did run without mutex?
> > > > > Do we really want to change this?
> > > > >
> > > >
> > > > I dont understand you. Original code does wakeup() outside mutex. I
> > > > moved wakeup() under mutex. You want to move it back?
> > >
> > > I just wanted to know why you moved it.
> > >
> > > Now I see. You use msleep_nsec() with timeout_mutex. Putting
> > > wakeup in mutex ensures that you don't miss it.
> >
> > Do we actually need to move the softclock() wakeup calls into the
> > mutex? As long as CIRCQ_EMPTY(...) is evaluated within timeout_mutex,
> > the thread can't get stuck waiting for a wakeup that isn't coming.
> > Both threads now sleep via msleep_nsec(), so there is no "gap" between
> > evaluation and unlock.
> >
> > Am I missing something else?
>
> In other hand, why to not move them under the `timeout_mutex' mutex(9)?
> Does this unlocked call provides something significant?
If you want to move the wakeups into timeout_mutex, let's do it in a
separate patch.
However, near as I can tell, keeping the calls where they are is still
correct. Please speak up if this is not true.
And note that all the wakeup() and softintr_schedule() calls are
currently made outside of timeout_mutex. Moving them for no reason
feels like we are buying trouble.
> > > Nitpick: timeoutmp_proc should be timeout_procmp. timeout_ is the
> > > prefix in this file. mp suffix is easier to see at the end.
> > >
> > > >+ if (kthread_create(softclockmp_thread, NULL, NULL, "softclockm"))
> > > "softclockm" -> "softclockmp"
> > >
> > > OK bluhm@, but let's wait for cheloha@ and see what he thinks
> >
> > Revised patch:
> >
> > - Add TIMEOUT_MPSAFE support to timeout_barrier(). This is crucial.
> > - Keep the names in the existing namespaces where possible.
> > - Keep the wakeup(9) calls in softclock() outside of timeout_mutex.
> > ... unless I have made an error, they can stay where they are.
> > - Trim the processing loops in the threads.
> > - Tweak the ddb(4) printing code to distinguish the locked and
> > unlocked thread circqs.
> >
> > mvs/bluhm: try this with your favorite process-context timeout and
> > make sure the timeouts still run.
> >
> > Assuming everything works, ok?
> >
>
> ok by me, with the one nit:
>
> > + msleep_nsec(&timeout_proc, &timeout_mutex, PSWP, "bored",
> > + INFSLP);
>
> "bored" is used by tasks. Can you use another ident?
"tmoslp" matches up with the "tmobar" wmesg in timeout_barrier(), so
let's try "tmoslp".
I will commit this tomorrow unless I hear otherwise.
Index: share/man/man9/timeout.9
===================================================================
RCS file: /cvs/src/share/man/man9/timeout.9,v
retrieving revision 1.56
diff -u -p -r1.56 timeout.9
--- share/man/man9/timeout.9 1 Jan 2023 01:19:18 -0000 1.56
+++ share/man/man9/timeout.9 12 Oct 2023 02:06:29 -0000
@@ -193,11 +193,16 @@ Counts the time elapsed since the system
The timeout's behavior may be configured with the bitwise OR of
zero or more of the following
.Fa flags :
-.Bl -tag -width TIMEOUT_PROC
+.Bl -tag -width TIMEOUT_MPSAFE
.It Dv TIMEOUT_PROC
Execute the timeout in a process context instead of the default
.Dv IPL_SOFTCLOCK
interrupt context.
+.It Dv TIMEOUT_MPSAFE
+Execute the timeout without the kernel lock.
+Requires the
+.Dv TIMEOUT_PROC
+flag.
.El
.El
.Pp
@@ -367,8 +372,9 @@ The function
.Fa fn
must not block and must be safe to execute on any CPU in the system.
.Pp
-Currently,
-all timeouts are executed under the kernel lock.
+Timeouts without the
+.Dv TIMEOUT_MPSAFE
+flag are executed under the kernel lock.
.Sh RETURN VALUES
.Fn timeout_add ,
.Fn timeout_add_sec ,
Index: sys/sys/timeout.h
===================================================================
RCS file: /cvs/src/sys/sys/timeout.h,v
retrieving revision 1.47
diff -u -p -r1.47 timeout.h
--- sys/sys/timeout.h 31 Dec 2022 16:06:24 -0000 1.47
+++ sys/sys/timeout.h 12 Oct 2023 02:06:29 -0000
@@ -54,6 +54,7 @@ struct timeout {
#define TIMEOUT_ONQUEUE 0x02 /* on any timeout queue */
#define TIMEOUT_INITIALIZED 0x04 /* initialized */
#define TIMEOUT_TRIGGERED 0x08 /* running or ran */
+#define TIMEOUT_MPSAFE 0x10 /* run without kernel lock */
struct timeoutstat {
uint64_t tos_added; /* timeout_add*(9) calls */
Index: sys/kern/kern_timeout.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_timeout.c,v
retrieving revision 1.95
diff -u -p -r1.95 kern_timeout.c
--- sys/kern/kern_timeout.c 29 Jul 2023 06:52:08 -0000 1.95
+++ sys/kern/kern_timeout.c 12 Oct 2023 02:06:29 -0000
@@ -75,6 +75,9 @@ struct circq timeout_wheel_kc[BUCKETS];
struct circq timeout_new; /* [T] New, unscheduled timeouts */
struct circq timeout_todo; /* [T] Due or needs rescheduling */
struct circq timeout_proc; /* [T] Due + needs process context */
+#ifdef MULTIPROCESSOR
+struct circq timeout_proc_mp; /* [T] Process ctx + no kernel lock */
+#endif
time_t timeout_level_width[WHEELCOUNT]; /* [I] Wheel level width
(seconds) */
struct timespec tick_ts; /* [I] Length of a tick (1/hz secs) */
@@ -171,6 +174,9 @@ void softclock_create_thread(void *);
void softclock_process_kclock_timeout(struct timeout *, int);
void softclock_process_tick_timeout(struct timeout *, int);
void softclock_thread(void *);
+#ifdef MULTIPROCESSOR
+void softclock_thread_mp(void *);
+#endif
void timeout_barrier_timeout(void *);
uint32_t timeout_bucket(const struct timeout *);
uint32_t timeout_maskwheel(uint32_t, const struct timespec *);
@@ -228,6 +234,9 @@ timeout_startup(void)
CIRCQ_INIT(&timeout_new);
CIRCQ_INIT(&timeout_todo);
CIRCQ_INIT(&timeout_proc);
+#ifdef MULTIPROCESSOR
+ CIRCQ_INIT(&timeout_proc_mp);
+#endif
for (b = 0; b < nitems(timeout_wheel); b++)
CIRCQ_INIT(&timeout_wheel[b]);
for (b = 0; b < nitems(timeout_wheel_kc); b++)
@@ -261,10 +270,16 @@ void
timeout_set_flags(struct timeout *to, void (*fn)(void *), void *arg, int
kclock,
int flags)
{
+ KASSERT(!ISSET(flags, ~(TIMEOUT_PROC | TIMEOUT_MPSAFE)));
+
to->to_func = fn;
to->to_arg = arg;
to->to_kclock = kclock;
to->to_flags = flags | TIMEOUT_INITIALIZED;
+
+ /* For now, only process context timeouts may be marked MP-safe. */
+ if (ISSET(to->to_flags, TIMEOUT_MPSAFE))
+ KASSERT(ISSET(to->to_flags, TIMEOUT_PROC));
}
void
@@ -455,13 +470,13 @@ timeout_barrier(struct timeout *to)
{
struct timeout barrier;
struct cond c;
- int procflag;
+ int flags;
- procflag = (to->to_flags & TIMEOUT_PROC);
- timeout_sync_order(procflag);
+ flags = to->to_flags & (TIMEOUT_PROC | TIMEOUT_MPSAFE);
+ timeout_sync_order(ISSET(flags, TIMEOUT_PROC));
timeout_set_flags(&barrier, timeout_barrier_timeout, &c, KCLOCK_NONE,
- procflag);
+ flags);
barrier.to_process = curproc->p_p;
cond_init(&c);
@@ -469,16 +484,26 @@ timeout_barrier(struct timeout *to)
barrier.to_time = ticks;
SET(barrier.to_flags, TIMEOUT_ONQUEUE);
- if (procflag)
- CIRCQ_INSERT_TAIL(&timeout_proc, &barrier.to_list);
- else
+ if (ISSET(flags, TIMEOUT_PROC)) {
+#ifdef MULTIPROCESSOR
+ if (ISSET(flags, TIMEOUT_MPSAFE))
+ CIRCQ_INSERT_TAIL(&timeout_proc_mp, &barrier.to_list);
+ else
+#endif
+ CIRCQ_INSERT_TAIL(&timeout_proc, &barrier.to_list);
+ } else
CIRCQ_INSERT_TAIL(&timeout_todo, &barrier.to_list);
mtx_leave(&timeout_mutex);
- if (procflag)
- wakeup_one(&timeout_proc);
- else
+ if (ISSET(flags, TIMEOUT_PROC)) {
+#ifdef MULTIPROCESSOR
+ if (ISSET(flags, TIMEOUT_MPSAFE))
+ wakeup_one(&timeout_proc_mp);
+ else
+#endif
+ wakeup_one(&timeout_proc);
+ } else
softintr_schedule(softclock_si);
cond_wait(&c, "tmobar");
@@ -659,7 +684,12 @@ softclock_process_kclock_timeout(struct
if (!new && timespeccmp(&to->to_abstime, &kc->kc_late, <=))
tostat.tos_late++;
if (ISSET(to->to_flags, TIMEOUT_PROC)) {
- CIRCQ_INSERT_TAIL(&timeout_proc, &to->to_list);
+#ifdef MULTIPROCESSOR
+ if (ISSET(to->to_flags, TIMEOUT_MPSAFE))
+ CIRCQ_INSERT_TAIL(&timeout_proc_mp, &to->to_list);
+ else
+#endif
+ CIRCQ_INSERT_TAIL(&timeout_proc, &to->to_list);
return;
}
timeout_run(to);
@@ -681,7 +711,12 @@ softclock_process_tick_timeout(struct ti
if (!new && delta < 0)
tostat.tos_late++;
if (ISSET(to->to_flags, TIMEOUT_PROC)) {
- CIRCQ_INSERT_TAIL(&timeout_proc, &to->to_list);
+#ifdef MULTIPROCESSOR
+ if (ISSET(to->to_flags, TIMEOUT_MPSAFE))
+ CIRCQ_INSERT_TAIL(&timeout_proc_mp, &to->to_list);
+ else
+#endif
+ CIRCQ_INSERT_TAIL(&timeout_proc, &to->to_list);
return;
}
timeout_run(to);
@@ -699,6 +734,9 @@ softclock(void *arg)
{
struct timeout *first_new, *to;
int needsproc, new;
+#ifdef MULTIPROCESSOR
+ int need_proc_mp;
+#endif
first_new = NULL;
new = 0;
@@ -719,10 +757,17 @@ softclock(void *arg)
}
tostat.tos_softclocks++;
needsproc = !CIRCQ_EMPTY(&timeout_proc);
+#ifdef MULTIPROCESSOR
+ need_proc_mp = !CIRCQ_EMPTY(&timeout_proc_mp);
+#endif
mtx_leave(&timeout_mutex);
if (needsproc)
wakeup(&timeout_proc);
+#ifdef MULTIPROCESSOR
+ if (need_proc_mp)
+ wakeup(&timeout_proc_mp);
+#endif
}
void
@@ -730,6 +775,10 @@ softclock_create_thread(void *arg)
{
if (kthread_create(softclock_thread, NULL, NULL, "softclock"))
panic("fork softclock");
+#ifdef MULTIPROCESSOR
+ if (kthread_create(softclock_thread_mp, NULL, NULL, "softclockmp"))
+ panic("kthread_create softclock_thread_mp");
+#endif
}
void
@@ -751,11 +800,8 @@ softclock_thread(void *arg)
sched_peg_curproc(ci);
s = splsoftclock();
+ mtx_enter(&timeout_mutex);
for (;;) {
- sleep_setup(&timeout_proc, PSWP, "bored");
- sleep_finish(0, CIRCQ_EMPTY(&timeout_proc));
-
- mtx_enter(&timeout_mutex);
while (!CIRCQ_EMPTY(&timeout_proc)) {
to = timeout_from_circq(CIRCQ_FIRST(&timeout_proc));
CIRCQ_REMOVE(&to->to_list);
@@ -763,11 +809,36 @@ softclock_thread(void *arg)
tostat.tos_run_thread++;
}
tostat.tos_thread_wakeups++;
- mtx_leave(&timeout_mutex);
+ msleep_nsec(&timeout_proc, &timeout_mutex, PSWP, "tmoslp",
+ INFSLP);
}
splx(s);
}
+#ifdef MULTIPROCESSOR
+void
+softclock_thread_mp(void *arg)
+{
+ struct timeout *to;
+
+ KERNEL_ASSERT_LOCKED();
+ KERNEL_UNLOCK();
+
+ mtx_enter(&timeout_mutex);
+ for (;;) {
+ while (!CIRCQ_EMPTY(&timeout_proc_mp)) {
+ to = timeout_from_circq(CIRCQ_FIRST(&timeout_proc_mp));
+ CIRCQ_REMOVE(&to->to_list);
+ timeout_run(to);
+ tostat.tos_run_thread++;
+ }
+ tostat.tos_thread_wakeups++;
+ msleep_nsec(&timeout_proc_mp, &timeout_mutex, PSWP, "tmoslp",
+ INFSLP);
+ }
+}
+#endif /* MULTIPROCESSOR*/
+
#ifndef SMALL_KERNEL
void
timeout_adjust_ticks(int adj)
@@ -875,6 +946,10 @@ db_show_timeout(struct timeout *to, stru
where = "softint";
else if (bucket == &timeout_proc)
where = "thread";
+#ifdef MULTIPROCESSOR
+ else if (bucket == &timeout_proc_mp)
+ where = "thread-mp";
+#endif
else {
if (to->to_kclock != KCLOCK_NONE)
wheel = timeout_wheel_kc;
@@ -888,11 +963,11 @@ db_show_timeout(struct timeout *to, stru
if (to->to_kclock != KCLOCK_NONE) {
kc = &timeout_kclock[to->to_kclock];
timespecsub(&to->to_abstime, &kc->kc_lastscan, &remaining);
- db_printf("%20s %8s %7s 0x%0*lx %s\n",
+ db_printf("%20s %8s %9s 0x%0*lx %s\n",
db_timespec(&remaining), db_kclock(to->to_kclock), where,
width, (ulong)to->to_arg, name);
} else {
- db_printf("%20d %8s %7s 0x%0*lx %s\n",
+ db_printf("%20d %8s %9s 0x%0*lx %s\n",
to->to_time - ticks, "ticks", where,
width, (ulong)to->to_arg, name);
}
@@ -913,11 +988,14 @@ db_show_callout(db_expr_t addr, int hadd
db_timespec(&kc->kc_lastscan), db_kclock(i));
}
db_printf("\n");
- db_printf("%20s %8s %7s %*s %s\n",
+ db_printf("%20s %8s %9s %*s %s\n",
"remaining", "clock", "wheel", width, "arg", "func");
db_show_callout_bucket(&timeout_new);
db_show_callout_bucket(&timeout_todo);
db_show_callout_bucket(&timeout_proc);
+#ifdef MULTIPROCESSOR
+ db_show_callout_bucket(&timeout_proc_mp);
+#endif
for (b = 0; b < nitems(timeout_wheel); b++)
db_show_callout_bucket(&timeout_wheel[b]);
for (b = 0; b < nitems(timeout_wheel_kc); b++)
