Message-ID: <414776CE.5030302@yahoo.com.au>
Date: Wed, 15 Sep 2004 08:55:10 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Ingo Molnar <mingo@elte.hu>
CC: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [patch] sched: fix scheduling latencies for !PREEMPT kernels
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Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> 
> 
>>Another thing, I don't mean this to sound like a rhetorical question,
>>but if we have a preemptible kernel, why is it a good idea to sprinkle
> 
>       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
>>cond_rescheds everywhere? Isn't this now the worst of both worlds? Why
>>would someone who really cares about latency not enable preempt?
> 
> 
> two things:
> 
> 1) none of the big distros enables CONFIG_PREEMPT in their kernels - not
> even SuSE. This is pretty telling.
> 
> 2) 10 new cond_resched()'s are not precisely 'sprinkle everywhere'.
> 

No, but I mean putting them right down into fastpaths like the vmscan
one, for example.

And if I remember correctly, you resorted to putting them into
might_sleep as well (but I haven't read the code for a while, maybe
you're now getting decent results without doing that).
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