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

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Message-ID: <alpine.LFD.1.10.0804250915340.2779@woody.linux-foundation.org>
Date:	Fri, 25 Apr 2008 09:24:11 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	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,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	pageexec@...email.hu, "H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH 1/1] x86: fix text_poke

On Fri, 25 Apr 2008, Andi Kleen wrote:
> 
> Not sure how the fixmap is better. It's pretty much equivalent, isn't it?
> Perhaps a little cheaper, but the code shouldn't be performance critical.

I have no really strong opinions. However, we do have a *lot* of lock 
prefixes in the kernel, and fixmaps are a lot cheaper than vmap(). It may 
not be performance-critical, but for me the "locks" section for the kernel 
is 0x8060 bytes long, which would seem to say that this is called four 
thousand times for each suspend and resume.

With each invocation being thousands of instructions and a cross-CPU IPI 
for the tlb flush, that kind of stuff adds up. We're likely talking real 
fractions of a second, rather than milliseconds.

But no, I didn't time it or really think very deeply about it.

		Linus
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