linux-kernel - Re: [PATCH v5 8/9] x86-64: Emulate legacy vsyscalls

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Date:	Mon, 06 Jun 2011 18:19:36 +0200
From:	pageexec@...email.hu
To:	Ingo Molnar <mingo@...e.hu>
CC:	Andrew Lutomirski <luto@....edu>, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Jesper Juhl <jj@...osbits.net>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Andi Kleen <andi@...stfloor.org>,
	Brian Gerst <brgerst@...il.com>,
	Louis Rilling <Louis.Rilling@...labs.com>,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH v5 8/9] x86-64: Emulate legacy vsyscalls

On 6 Jun 2011 at 17:59, Ingo Molnar wrote:

> > > FYI, incredible amount of work has gone into making pagefaults as 
> > > fast and scalable as possible.
> > 
> > i wasn't talking about scalability (it's irrelevant anyway here), 
> > only speed. [...]
> 
> Which part of "fast and scalable" did you not understand?

uhm, not sure why you're so worked up here. is it because i said
'scalability' was completely irrelevant for the nx vsyscall page
approach? elaborate!

> Just a couple of days ago i noticed a single cycle inefficiency in 
> the pagefault fastpath, introduced in the 3.0 merge window. I 
> requested (and got) an urgent fix for that:

so you must have measurements. what's the mentioned page faults take
in cycles before/after your fix? what's a normal int xx path take?

> So i ask you again, what is your basis for calling the #PF path on 
> Linux a 'slowpath'? Is Linus's and my word and 5 years of Git history 
> showing that it's optimized as a fastpath not enough proof for you?

which part of

> you must have realized by now that slow/fast path in this context were
> relative to int xx vs. pf processing.

did you not understand? do you have "Linus's and my word and 5 years of
Git history" to show that pf processing is seriously that much faster
than int xx processing?

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