Date: Thu, 30 Sep 2004 14:30:51 -0400 From: Stephan Uphoff <ups@tree.com> To: John Baldwin <jhb@FreeBSD.org> Cc: "freebsd-arch@freebsd.org" <freebsd-arch@FreeBSD.org> Subject: Re: scheduler (sched_4bsd) questions Message-ID: <1096569051.21577.23.camel@palm.tree.com> In-Reply-To: <200409301017.54350.jhb@FreeBSD.org> References: <1095468747.31297.241.camel@palm.tree.com> <200409291652.29990.jhb@FreeBSD.org> <1096496057.3733.2163.camel@palm.tree.com> <200409301017.54350.jhb@FreeBSD.org>
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On Thu, 2004-09-30 at 10:17, John Baldwin wrote:
> Fair enough. The right place to fix this is in turnstile_unpend() though I
> think. I have had these patches that try to "clump" setrunqueue's before
> preempting lying around (but not thoroughly tested yet) that might fix this
> as well but in the turnstile code itself:
- snip -
> --- //depot/projects/smpng/sys/kern/subr_turnstile.c 2004/09/03 14:14:21
> +++ //depot/user/jhb/preemption/kern/subr_turnstile.c 2004/09/10 21:36:10
> @@ -727,6 +726,7 @@
> * in turnstile_wait(). Set a flag to force it to try to acquire
> * the lock again instead of blocking.
> */
> + critical_enter();
> while (!TAILQ_EMPTY(&pending_threads)) {
> td = TAILQ_FIRST(&pending_threads);
> TAILQ_REMOVE(&pending_threads, td, td_lockq);
> @@ -742,6 +742,7 @@
> MPASS(TD_IS_RUNNING(td) || TD_ON_RUNQ(td));
> }
> }
> + critical_exit();
> mtx_unlock_spin(&sched_lock);
> }
-snip -
>
> I.e., you could just move the critical_enter() in subr_turnstile.c earlier so
> it is before the mtx_unlock_spin() of the turnstile chain lock.
I agree - this would be the right place.
I was originally planning to do some more work in kern_mutex and did not
want to touch more than one file ;-)
Can you check this in?
Your other patches look like they are targeted to avoid senseless
switching to improve performance - but should not have an impact on
correct function. Right ?
Hopefully I get some time to look at them more closely later on.
Stephan
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