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Subject: Re: [PATCH] perf_counter: Prevent oopses from per-cpu software
	counters
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
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Date: Fri, 06 Feb 2009 14:35:25 +0800
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On Fri, 2009-02-06 at 15:34 +1100, Paul Mackerras 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.
> 
> It looks like the scheduler doesn't keep per-cpu counts of context
> switches
rq->sched_switch or sched_count? sched_switch is defined, but not used. They
all depends on CONFIG_SCHEDSTATS=y.

>  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?
> 
> Paul.