linux-kernel - Re: [patch] sched: schedstat needs a diet

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Message-ID: <20071017072323.GB18044@elte.hu>
Date:	Wed, 17 Oct 2007 09:23:24 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Ken Chen <kenchen@...gle.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch] sched: schedstat needs a diet


* Ken Chen <kenchen@...gle.com> wrote:

> schedstat is useful in investigating CPU scheduler behavior.  Ideally, 
> I think it is beneficial to have it on all the time.  However, the 
> cost of turning it on in production system is quite high, largely due 
> to number of events it collects and also due to its large memory 
> footprint.
> 
> Most of the fields probably don't need to be full 64-bit on 64-bit 
> arch.  Rolling over 4 billion events will most like take a long time 
> and user space tool can be made to accommodate that.  I'm proposing 
> kernel to cut back most of variable width on 64-bit system.  (note, 
> the following patch doesn't affect 32-bit system).

thanks, applied.

note that current -git has a whole bunch of new schedstats fields in 
/proc/<PID>/sched which can be used to track the exact balancing 
behavior of tasks. It can be cleared via echoing 0 to the file - so 
overflow is not an issue. Most of those new fields should probably be 
unsigned int too. (they are u64 right now.)

	Ingo
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