From: Ingo Molnar <mingo@elte.hu>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>,
peterz@infradead.org, fweisbec@gmail.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] [lockup detector] sync touch_*_watchdog back to old semantics
Date: Wed, 1 Sep 2010 09:20:16 +0200 [thread overview]
Message-ID: <20100901072016.GA27065@elte.hu> (raw)
In-Reply-To: <AANLkTim1s=O6+OEvwLsaxbkpfyQk-Mypr5wE7H4fh9V0@mail.gmail.com>
* Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> On 9/1/10, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> > On 9/1/10, Ingo Molnar <mingo@elte.hu> wrote:
> >>
> >> * Don Zickus <dzickus@redhat.com> wrote:
> >>
> >>> void touch_nmi_watchdog(void)
> >>> {
> >>> - __get_cpu_var(watchdog_nmi_touch) = true;
> >>> + if (watchdog_enabled) {
> >>> + unsigned cpu;
> >>> +
> >>> + for_each_present_cpu(cpu) {
> >>> + if (per_cpu(watchdog_nmi_touch, cpu) != true)
> >>> + per_cpu(watchdog_nmi_touch, cpu) = true;
> >>> + }
> >>
> >> Hm, this is going to be a scalability nightmare with lots of CPUs. Not
> >> only do we have a nr_cpus loop, but we touch per-cpu areas of _other_
> >> CPUs - a big scalability nono.
> >>
> >> Why do we need to do this? We never needed to touch other CPU's NMI
> >> lockup accounting data areas - why has this changed? The changelog does
> >> not explain this.
> >>
> >> Thanks,
> >>
> >> Ingo
> >>
> > I believe this came from old nmi watchdog code where it might be
> > useful when nmi watchdog activated via io-apic. I'm trying to figure
> > out if we really need it still.
>
> Well, we can't drop it or make per-cpu specific, for example we need
> it in case of panic with watchdog enabled and panic timeout set, or
> boot delay set and etc. Seems same applies to printk_delay. Hmm...
Ok - can you cite the old watchdog code, did it really do a nr_cpus
loop?
Thanks,
Ingo
next prev parent reply other threads:[~2010-09-01 7:20 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-01 3:00 [PATCH 0/3] lockup detector fixes Don Zickus
2010-09-01 3:00 ` [PATCH 1/3] [lockup detector] sync touch_*_watchdog back to old semantics Don Zickus
2010-09-01 5:30 ` Ingo Molnar
2010-09-01 6:00 ` Cyrill Gorcunov
2010-09-01 7:01 ` Cyrill Gorcunov
2010-09-01 7:20 ` Ingo Molnar [this message]
2010-09-01 7:42 ` Cyrill Gorcunov
2010-09-01 9:19 ` [tip:perf/urgent] lockup_detector: Sync " tip-bot for Don Zickus
2010-09-01 3:00 ` [PATCH 2/3] lockup_detector: convert cpu notifier to return encapsulate errno value Don Zickus
2010-09-01 6:24 ` [tip:perf/core] lockup_detector: Convert " tip-bot for Akinobu Mita
2010-09-01 3:00 ` [PATCH 3/3] lockup_detector: remove unnecessary panic_notifier Don Zickus
2010-09-01 6:25 ` [tip:perf/core] lockup_detector: Remove unused panic_notifier tip-bot for Akinobu Mita
-- strict thread matches above, loose matches on Subject: below --
2010-09-01 15:51 [PATCH 1/3] [lockup detector] sync touch_*_watchdog back to old semantics Don Zickus
2010-09-01 16:36 ` Cyrill Gorcunov
2010-09-01 17:15 ` Ingo Molnar
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