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 09:30:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
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


* 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
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