linux-kernel - Re: [PATCH 3/2] perf tools: Use DECLARE_BITMAP instead of an open-coded array

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Date:	Mon, 19 Oct 2009 21:40:23 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 3/2] perf tools: Use DECLARE_BITMAP instead of an
	open-coded array

On Mon, Oct 19, 2009 at 09:30:39AM +0200, Ingo Molnar wrote:
> 
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > On Sat, Oct 17, 2009 at 05:57:18PM +0200, Frederic Weisbecker wrote:
> > > Use DECLARE_BITMAP instead of an open coded array for our bitmap
> > > of featured sections.
> > > 
> > > This makes the array an unsigned long instead of a u64 but since we 
> > > use a 256 bits bitmap, the array size shouldn't vary between 
> > > different boxes.
> > 
> > That said I would really feel more comfortable if someone can confirm 
> > that.
> 
> Should be size-invariant for the bitmap size of 256 bits due to:
> 
> #define DECLARE_BITMAP(name,bits) \
>         unsigned long name[BITS_TO_LONGS(bits)]
> 
> but it's not little-endian/big-endian invariant.
> 
> We should at minimum save the CPU architecture (and endianness 
> parameters) the data got generated on, and reject 
> endianness-incompatible uses - so that if someone wants to add 
> cross-endian support it can be implemented cleanly.
> 
> 	Ingo


Oh right, I'll add an endianness field then.

Thanks.

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