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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