Message-ID: <40741819.5060001@yahoo.com.au>
Date: Thu, 08 Apr 2004 01:02:49 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Paul Jackson <pj@sgi.com>
CC: vda@port.imtp.ilyichevsk.odessa.ua, colpatch@us.ibm.com,
       wli@holomorphy.com, linux-kernel@vger.kernel.org
Subject: Re: [Patch 17/23] mask v2 = [6/7] nodemask_t_ia64_changes
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Paul Jackson wrote:
> Nick wrote:
> 
>>No, the schedule() fastpath doesn't use find_next_bit. 
> 
> 
> Ok - makes sense - thanks.
> 
> Uninlining it is perhaps the easiest way out.
> 
> That or replacing it with the trivial version that is several times
> smaller (loops one bit at a time, checking 'test_bit()').
> 
> Right now, I don't see any excuse for that fat version of find_next_bit()
> to exist.
> 

Well it would be nice to keep it fast though, especially
for big masks like those 64 byte cpumasks of yours. In
the scheduler for example, a lot of balancing operations
are done with very sparse cpumasks, which your bit at a
time version doesn't handle very well.

For example, a global CPU balancing operation on a 512
CPU system with 2 CPUs per node currently does 256
for_each_cpu loops over cpumasks with two entries in
them. 130 thousand test_bit loop iteratinos.

The uninlined larger version would have to be smaller and
faster than your small version inlined, wouldn't it?
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