linux-kernel - Re: [PATCH] perf_counter: Prevent oopses from per-cpu software counters

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Message-ID: <18827.48582.613391.869829@cargo.ozlabs.ibm.com>
Date:	Fri, 6 Feb 2009 15:34:14 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf_counter: Prevent oopses from per-cpu software
	counters

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 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.
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