linux-kernel - Re: [PATCH 02/16] perf: Add ability to attach registers dump to sample

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Date:	Thu, 24 May 2012 11:51:50 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	acme@...hat.com, mingo@...e.hu, paulus@...ba.org,
	cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	eranian@...gle.com, gorcunov@...nvz.org, tzanussi@...il.com,
	mhiramat@...hat.com, robert.richter@....com, fche@...hat.com,
	linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
	drepper@...il.com, asharma@...com, benjamin.redelings@...cent.org
Subject: Re: [PATCH 02/16] perf: Add ability to attach registers dump to
 sample

On Wed, 2012-05-23 at 21:32 +0200, Jiri Olsa wrote:
> +perf_output_sample_regs(struct perf_output_handle *handle,
> +                       struct pt_regs *regs, u64 mask)
> +{
> +       int i = 0;
> +
> +       do {
> +               u64 val;
> +
> +               if (mask & 1) {
> +                       val = perf_reg_value(regs, i);
> +                       perf_output_put(handle, val);
> +               }
> +
> +               mask >>= 1;
> +               i++;
> +       } while (mask);
> +} 

we have bitmap functions available that can do this far faster on a
number of architectures (like x86) that have bit scanning instructions.

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