Messages in this thread | | | Date | Wed, 1 Sep 2010 11:01:06 +0400 | Subject | Re: [PATCH 1/3] [lockup detector] sync touch_*_watchdog back to old semantics | From | Cyrill Gorcunov <> |
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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...
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