linux-kernel - Re: [PATCH 1/2] perf tools: Fix sample size bit operations

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Date:	Mon, 23 May 2011 13:28:15 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/2] perf tools: Fix sample size bit operations


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> What we want is to count the number of bits in the mask,
> not some other random operation written in the middle
> of the night.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Stephane Eranian <eranian@...gle.com>
> ---
>  tools/perf/util/event.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index 17c1c3c..d3fa7e4 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -42,7 +42,7 @@ int perf_sample_size(u64 sample_type)
>  	int i;
>  
>  	for (i = 0; i < 64; i++) {
> -		if ((mask << i) & 1)
> +		if (mask & (1 << i))
>  			size++;
>  	}

I fixed this to be 1UL and applied your fixes out of email - perf top and perf 
report works fine now, so this was a 64-bitness bug (you probably used a 32-bit 
system for testing?).

Btw., shouldnt this use hweight() or such?

Thanks,

	Ingo
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