linux-kernel - Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native 64-bit

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Message-ID: <CALCETrUNd3quHegbyaoqRT27gazhR0QBpm7PUxxH1tg=ZC-MTg@mail.gmail.com>
Date:	Tue, 6 Oct 2015 11:26:43 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>, X86 ML <x86@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native 64-bit

On Oct 6, 2015 1:39 AM, "Linus Torvalds" <torvalds@...ux-foundation.org> wrote:
>
> On Tue, Oct 6, 2015 at 1:47 AM, Andy Lutomirski <luto@...nel.org> wrote:
> >
> > The patchset is structured as a removal of the old fast syscall
> > code, then the change that makes syscalls into real functions, then
> > a clean re-implementation of fast syscalls.
> >
> > If we want some of the 25 cycles back, we could consider open-coding
> > a new C fast path.
>
> Ok, the 25 cycles are apparently just 12 cycles. Did you forget to
> update that after doing some of the optimizations - or is it 25 cycles
> on 64-bit and 12 cycles on 32-bit?

Forgot to update.  I'll fix this in v3.  I'll also re-benchmark on
native 32-bit, which is a bit easier now that I figured out why my
Debian VM couldn't do fast syscalls.  (Hint: if you have a 32-bit
Debian or Debian-derived setup without libc6-i686 installed, install
it and everything works better.)

--Andy
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