From: Ingo Molnar <mingo@elte.hu>
To: Paul Mackerras <paulus@samba.org>
Cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] perf_counter: Prevent oopses from per-cpu software counters
Date: Fri, 6 Feb 2009 16:31:38 +0100 [thread overview]
Message-ID: <20090206153138.GM18368@elte.hu> (raw)
In-Reply-To: <18827.48582.613391.869829@cargo.ozlabs.ibm.com>
* Paul Mackerras <paulus@samba.org> wrote:
> Ingo Molnar writes:
>
> > So how about fixing these sw counts to properly work as percpu counters too?
>
> OK, so for page faults it looks like I want to look at
>
> get_cpu_var(vm_event_states).event[PGFAULT]
>
> to get the per-cpu page fault count, as long as
> CONFIG_VM_EVENT_COUNTERS is set.
Yeah - i'd suggest that. Note hat VM_EVENT_COUNTERS is default enabled on
99.99% of kernels:
config VM_EVENT_COUNTERS
default y
bool "Enable VM event counters for /proc/vmstat" if EMBEDDED
> It looks like the scheduler doesn't keep per-cpu counts of context
> switches or task migrations, or if it does I couldn't find them. We could
> do stuff in perf_counter_task_sched_in/out to implement per-cpu context
> switch and migration counters by adding up the delta values for each task
> that gets scheduled onto the cpu. Or we could add explicit per-cpu
> counters for these things in the scheduler.
>
> What do you think?
For per-cpu counts of context switches we already have rq->nr_switches.
We dont have per-cpu counts of migrations - but could add them.
We should do it this way becaue it would be nice to make per-cpu counters
work just fine even if they are never switched in and out during context
switches. That turns per-cpu counters into even lower-overhead ways of
monitoring those values.
Ingo
prev parent reply other threads:[~2009-02-06 15:32 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-05 4:52 [PATCH] perf_counter: Prevent oopses from per-cpu software counters Paul Mackerras
2009-02-05 14:22 ` Ingo Molnar
2009-02-06 2:40 ` Paul Mackerras
2009-02-06 4:34 ` Paul Mackerras
2009-02-06 6:35 ` Zhang, Yanmin
2009-02-06 15:31 ` Ingo Molnar [this message]
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