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

From: pageexec
Date: Mon Jun 06 2011 - 12:21:30 EST

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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