Date: Tue, 06 Nov 2012 09:28:37 +0800 From: David Xu <davidxu@freebsd.org> To: Andriy Gapon <avg@freebsd.org> Cc: Jeff Roberson <jroberson@jroberson.net>, current@freebsd.org Subject: Re: ULE patch, call for testers Message-ID: <509867C5.6030109@freebsd.org> In-Reply-To: <50978353.7090204@FreeBSD.org> References: <alpine.BSF.2.00.1211020822260.1947@desktop> <50972740.7000703@freebsd.org> <50978353.7090204@FreeBSD.org>
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On 2012/11/05 17:13, Andriy Gapon wrote: > 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); > > What I want is fairness between waiting on runqueue and waiting on sleepqueue. Supports you have N threads on runqueue: T1,T2,T3...Tn. and a thread T(n+1) on sleepqueue. If CPU runs threads T1...Tn in round-robin fashion, and suppose at time n, the thread Tn is run, this means total time of n-1 is passed, and at the time, thread T(n+1) is woken up, and scheduler's sched_interact_score() will give it higher priority over Tn, this is unfair because both threads have spent same total time to waiting for cpu. Do your patch fix the problem ? Regards, David Xu
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