lkml.org 
[lkml]   [2007]   [Apr]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 3/8] Use process freezer for cpu-hotplug
Ingo Molnar wrote:
>
> * Nathan Lynch <ntl@pobox.com> wrote:
>
> > > - raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
> > > + if (freeze_processes(FE_HOTPLUG_CPU)) {
> > > + thaw_processes(FE_HOTPLUG_CPU);
> > > + return -EBUSY;
> > > + }
> > > +
> >
> > If I'm understanding correctly, this will cause
> >
> > # echo 0 > /sys/devices/system/cpu/cpuX/online
> >
> > to sometimes fail, and userspace is expected to try again? This will
> > break existing applications.
> >
> > Perhaps drivers/base/cpu.c:store_online should retry as long as
> > cpu_up/down return -EBUSY. That would avoid a userspace-visible
> > interface change.
>
> yeah. I'd even suggest a freeze_processes_nofail() API instead, that
> does this internally, without burdening the callsites. (and once the
> freezer becomes complete then freeze_processes_nofail() ==
> freeze_processes())

Yeah, I just realized that an implementation of my proposal would busy
loop in the kernel forever if a silly admin tried to offline the last
cpu (we're already using -EBUSY for that case), so
freeze_processes_nofail is a better idea :-)

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-04-06 19:49    [W:0.078 / U:2.864 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site