Date: Mon, 05 Nov 2012 11:13:55 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: David Xu <davidxu@FreeBSD.org>, Jeff Roberson <jroberson@jroberson.net> Cc: current@FreeBSD.org Subject: Re: ULE patch, call for testers Message-ID: <50978353.7090204@FreeBSD.org> In-Reply-To: <50972740.7000703@freebsd.org> References: <alpine.BSF.2.00.1211020822260.1947@desktop> <50972740.7000703@freebsd.org>
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on 05/11/2012 04:41 David Xu said the following:
> Another problem I remembered is that a thread on runqueue may be starved
> because ULE treats a sleeping thread and a thread waiting on runqueue
> differently. If a thread has slept for a while, after it is woken up,
> its priority is boosted, but for a thread on runqueue, its priority
> will never be boosted. In essential, they should be same becase both of
> them are waiting for cpu. If I am a thread, I'd like to wait on sleep
> queue rather than on runqueue, since in former case, I will get
> bonus, while in later case, I'll get nothing. Under heavy load,
> there are many runnable threads, this unfair can cause a very low priority
> thread on runqueue to be starved. 4BSD seems not suffer from
> this problem, because it also decay cpu time of thread on runqueue.
> I think ULE needs some anti-starvation code to give thread a shot
> if it is waiting on runqueue too long time.
I also noticed this issue and I've been playing with the following patch.
Two points:
o I am not sure if it is ideologically correct
o it didn't improve much the behavior of my workloads
In any case, here it is:
- extend accounted interactive sleep time to a point where a thread runs
(as opposed to be added to runq)
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -1898,8 +1899,21 @@ sched_switch(struct thread *td, struct thread *newtd, int
flags)
SDT_PROBE2(sched, , , off_cpu, td, td->td_proc);
lock_profile_release_lock(&TDQ_LOCKPTR(tdq)->lock_object);
TDQ_LOCKPTR(tdq)->mtx_lock = (uintptr_t)newtd;
+#if 1
+ /*
+ * If we slept for more than a tick update our interactivity and
+ * priority.
+ */
+ int slptick;
+ slptick = newtd->td_slptick;
+ newtd->td_slptick = 0;
+ if (slptick && slptick != ticks) {
+ newtd->td_sched->ts_slptime +=
+ (ticks - slptick) << SCHED_TICK_SHIFT;
+ sched_interact_update(newtd);
+ }
+#endif
sched_pctcpu_update(newtd->td_sched, 0);
-
#ifdef KDTRACE_HOOKS
/*
* If DTrace has set the active vtime enum to anything
@@ -1990,6 +2004,7 @@ sched_wakeup(struct thread *td)
THREAD_LOCK_ASSERT(td, MA_OWNED);
ts = td->td_sched;
td->td_flags &= ~TDF_CANSWAP;
+#if 0
/*
* If we slept for more than a tick update our interactivity and
* priority.
@@ -2001,6 +2016,7 @@ sched_wakeup(struct thread *td)
sched_interact_update(td);
sched_pctcpu_update(ts, 0);
}
+#endif
/* Reset the slice value after we sleep. */
ts->ts_slice = sched_slice;
sched_add(td, SRQ_BORING);
--
Andriy Gapon
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