linux-ext4 - Re: [PATCH 1/1] x86: fix text

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Message-ID: <481DE1D2.4080704@zytor.com>
Date:	Sun, 04 May 2008 09:18:26 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Jiri Slaby <jirislaby@...il.com>,
	David Miller <davem@...emloft.net>, zdenek.kabelac@...il.com,
	rjw@...k.pl, paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
	linux-ext4@...r.kernel.org, herbert@...dor.apana.org.au,
	penberg@...helsinki.fi, clameter@....com,
	linux-kernel@...r.kernel.org, pageexec@...email.hu
Subject: Re: [PATCH 1/1] x86: fix text_poke

Mathieu Desnoyers wrote:
> 
> I am not saying that the standard marker will have to inhibit
> optimizations. Actually, it's the contrary : a well-thought marker
> should _not_ modify that kind of optimization, and we should put markers
> in code locations less likely to inhibit gcc optimizations. However, in
> the case where we happen to be interested in information otherwise
> optimized away by GCC, it makes sense to inhibit this optimization in
> order to have the information available for tracing.
> 
> I expect this to happen rarely, but I think we must deal with
> optimizations to make sure we never trace garbage due to some unexpected
> gcc optimization. I think it's a small (e.g. undetectable at the
> macrobenchmark level) price to pay to get correct tracing information.
> 

That's a pretty flippant reply... liveness causes register pressure 
which can cause rapid degradation in code quality on a register-starved 
architecture like x86.

	-hpa
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