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In-Reply-To: <200906291934.56186.paul@codesourcery.com>
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Date: Mon, 29 Jun 2009 20:57:17 +0200
Message-ID: <5b31733c0906291157n7d8c56d4m9813cc090e42ba08@mail.gmail.com>
Subject: Re: [Qemu-devel] [PATCH 2/3] Get rid of temporary variable cache.
From: Filip Navara <filip.navara@gmail.com>
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To: Paul Brook <paul@codesourcery.com>
Cc: qemu-devel@nongnu.org

On Mon, Jun 29, 2009 at 8:34 PM, Paul Brook<paul@codesourcery.com> wrote:
> On Monday 29 June 2009, Filip Navara wrote:
>> The temporary variable cache actually hurts TCG more than it helps.
>> Empirical results show that when running the Dhrystone benchmark with this
>> patch improves the speed by about 2%.
>
> I find it hard to believe this patch has any significant effect on runtime,
> other than random variation. My guess is it spends almost all of its time in a
> few guest loops, and no time doing translation. I'd expect the generated code
> should be the same before and after.

You are right. That will teach me not to trust benchmarks and validate
the results by other means also.

> I'm not saying this patch is a bad idea (new_tmp/dead_tmp predate
> tcg_temp_free and are now redundant), just that I don't believe your benchmark
> results.

And you were right not to believe them. Thanks for looking at the patch.

Best regards,
Filip Navara