linux-kernel - Re: [GIT PULL] scheduler fixes

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Date:	Mon, 4 Apr 2011 21:38:45 +0530
From:	Sisir Koppaka <sisir.koppaka@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] scheduler fixes

On Mon, Apr 4, 2011 at 9:15 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> So I pulled this, but I think this:
>
> On Sat, Apr 2, 2011 at 3:31 AM, Ingo Molnar <mingo@...e.hu> wrote:
>>
>> -               if (interval > HZ*NR_CPUS/10)
>> -                       interval = HZ*NR_CPUS/10;
>> +               if (interval > HZ*num_online_cpus()/10)
>> +                       interval = HZ*num_online_cpus()/10;
>
> is a horrible patch.
>
> Think about what that expands to. It's going to potentially be two
> function calls. And the code is just ugly.
>
> So please, when doing search-and-replace changes like this, just clean
> up the code at the same time. Back when it was about pure constants,
> there was only a typing/ugly overhead from duplicating the constant,
> but the compiler would see a single constant.
>
> Now it's _possible_ that the compiler could do the analysis and fold
> it all back to a single thing. But it's unlikely to happen except for
> configurations that end up making it all trivial.
>
> So just add something like a
>
>   int max_interval = HZ*num_online_cpus()/10;
>
> possibly even with a comment about _why_ that is the max interval allowed.  Ok?
>
>                        Linus
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Ok sure. You're right, I'll resend the patch.
Sisir
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