Subject: Re: Dynamically determine if kernel includes CFS Scheduler
From: Peter Zijlstra <peterz@infradead.org>
To: Darren Hart <dvhltc@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>, "lkml," <linux-kernel@vger.kernel.org>
In-Reply-To: <49B18B2E.606@us.ibm.com>
References: <49B18B2E.606@us.ibm.com>
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Date: Fri, 06 Mar 2009 22:01:06 +0100
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On Fri, 2009-03-06 at 12:44 -0800, Darren Hart wrote:
> I've received an internal request for a means to determine at run-time 
> if the CFS scheduler is included in the running kernel.  Looking through 
> the git commit log and the /proc/sys/kernel filesystem, I think I see 
> two approaches:
> 
> 1) stat("/proc/sys/kernel/sched_compat_yield")
>     This confirms 2.6.23-rc7 kernel or later which definitely has the CFS
>     scheduler and this functionality is of interest anyway.
> 2) Test if the kernel version is >= 2.6.22 which is where I believe CFS
>     landed.
> 
> Any guesses as to how robust/future-proof approach #1 would be?

The question is why? Relying on scheduler specifics outside of whatever
POSIX mandates is an application bug.

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