linux-kernel - Re: [RFC] speeding up the stat() family of system calls...

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Message-ID: <52B8CE99.2050608@zytor.com>
Date:	Mon, 23 Dec 2013 16:00:25 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@...iv.linux.org.uk>
CC:	the arch/x86 maintainers <x86@...nel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] speeding up the stat() family of system calls...

On 12/21/2013 12:27 PM, Linus Torvalds wrote:
> 
> HOWEVER. On x86, doing an efficient field-at-a-time copy also requires
> us to use put_user_try() and put_user_catch() in order to not have
> tons of clac/stac instructions for the extended permission testing.
> And the implementation of that was actually fairly non-optimal, so to
> actually get the code I wanted, I had to change how that all worked
> too, using "asm_volatile_goto()".
> 

I guess I'm a bit puzzled... the current code should be just fine if
everything is present, and do we really care about the performance if we
actually have an error condition?

I'm a bit concerned about the put_user_fail: label having uniqueness
problem, which I know some versions of gcc at least get very noisy over.

I like the overall approach, however.

	-hpa

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