From: mikpe@csd.uu.se
To: Keith Owens <kaos@ocs.com.au>
Cc: mikpe@csd.uu.se, linux-kernel@vger.kernel.org
Subject: Re: [patch] 2.4.21-pre5 correct scheduling of idle tasks [ all arch ]
Date: Fri, 28 Mar 2003 11:10:28 +0100 [thread overview]
Message-ID: <16004.8084.271596.293605@gargle.gargle.HOWL> (raw)
In-Reply-To: <19527.1048803432@ocs3.intra.ocs.com.au>
Keith Owens writes:
> On Thu, 27 Mar 2003 16:54:47 +0100,
> mikpe@csd.uu.se wrote:
> >Keith Owens writes:
> > > There are several inconsistencies in the scheduling of idle tasks and,
> > > for UP, tracking which task is on the cpu. This patch standardizes
> > > idle task scheduling across all architectures and corrects the UP
> > > error, it is just a bug fix.
> >...
> > > To make it worse, on UP a task is assigned to a cpu but never released.
> > > Very quickly, all tasks are marked as currently running on cpu 0 :(.
> >
> >->cpus_runnable and task_has_cpu() are SMP-only, as a quick grep
> >through 2.4.20 will tell you. There is no UP bug here to fix.
>
> cpus_runnable has task_has_cpu are not guarded by CONFIG_SMP.
> task_set_cpu() is called for UP as well as SMP. UP is missing the
> corresponding call to task_release_cpu().
No generic kernel code _uses_ ->cpus_runnable on UP.
arch/s390{,x}/kernel/traps.c appears to use task_has_cpu() on UP,
but that's their bug and not an argument for slowing down UP kernels.
Hence, kernel/sched.c not calling task_release_cpu() to reset
->cpus_runnable to ~0 is not a bug.
The only bug (apart from s390's trap.c) is that task_set_cpu() performs
an unnecessary assignment to ->cpus_runnable on UP.
/Mikael
prev parent reply other threads:[~2003-03-28 9:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-03-26 6:10 Keith Owens
2003-03-27 15:54 ` mikpe
2003-03-27 22:17 ` Keith Owens
2003-03-28 10:10 ` mikpe [this message]
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