From: Andi Kleen <andi@firstfloor.org>
To: dean gaudet <odo@google.com>
Cc: Andi Kleen <andi@firstfloor.org>, Pardo <pardo@google.com>,
linux-kernel@vger.kernel.org, mbligh@google.com,
briangrant@google.com, nil@google.com, jyasskin@google.com
Subject: Re: Faster getcpu() and sched_getcpu()
Date: Mon, 29 Sep 2008 16:54:08 +0200 [thread overview]
Message-ID: <20080929145408.GQ25711@one.firstfloor.org> (raw)
In-Reply-To: <48E0834D.6010608@google.com>
On Mon, Sep 29, 2008 at 12:27:09AM -0700, dean gaudet wrote:
> Andi Kleen wrote:
> > I'm still not sure why you say no redzone is that expensive? Do you
> > have numbers? I know it's a few instructions, but it shouldn't
> > be that expensive.
> >
> >
>
> it depends on the processor involved and the kernel config options --
> i.e. if frame pointers are enabled then the stack frame guarantees a
> store operation (push rbp) and on processors which do memops in-order
> this delays the other memops in the vsyscall (i.e. testing the cache or
> executing SIDT). it was 2 or 3 cycles difference in most cases iirc.
Ok frame pointers are always a performance disasters on some CPUs.
Perhaps they should be just unconditionally disabled for vsyscall.c
and the vdso
-Andi
--
ak@linux.intel.com
next prev parent reply other threads:[~2008-09-29 14:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <af8810200809111648n55e05ac9g286fcd498690432f@mail.gmail.com>
2008-09-23 19:09 ` Faster getcpu() and sched_getcpu() Pardo
2008-09-23 19:48 ` Fwd: " Pardo
2008-09-28 16:42 ` Andi Kleen
2008-09-29 7:27 ` dean gaudet
2008-09-29 14:54 ` Andi Kleen [this message]
2008-09-29 18:02 ` Pardo
[not found] ` <af8810200809291101r6f3208beua36a4b2d3b5713eb@mail.gmail.com>
2008-09-29 20:50 ` Andi Kleen
[not found] ` <48E14ECE.6080402@google.com>
2008-09-29 21:59 ` dean gaudet
2008-09-29 22:07 ` Andi Kleen
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