From: Jens Axboe <jens.axboe@oracle.com>
To: Nick Piggin <npiggin@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: lmbench ctxsw regression with CFS
Date: Mon, 13 Aug 2007 14:30:31 +0200 [thread overview]
Message-ID: <20070813123031.GS23758@kernel.dk> (raw)
In-Reply-To: <20070806032949.GA16401@wotan.suse.de>
On Mon, Aug 06 2007, Nick Piggin wrote:
> > > What CPU did you get these numbers on? Do the indirect calls hurt much
> > > on those without an indirect predictor? (I'll try running some tests).
> >
> > it was on an older Athlon64 X2. I never saw indirect calls really
> > hurting on modern x86 CPUs - dont both CPU makers optimize them pretty
> > efficiently? (as long as the target function is always the same - which
> > it is here.)
>
> I think a lot of CPUs do. I think ia64 does not. It predicts
> based on the contents of a branch target register which has to
> be loaded I presume before instructoin fetch reaches the branch.
> I don't know if this would hurt or not.
Testing on ia64 showed that the indirect calls in the io scheduler hurt
quite a bit, so I'd be surprised if the impact here wasn't an issue
there.
--
Jens Axboe
next prev parent reply other threads:[~2007-08-13 14:59 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-02 2:15 lmbench ctxsw regression with CFS Nick Piggin
2007-08-02 2:31 ` Linus Torvalds
2007-08-02 2:41 ` Nick Piggin
2007-08-02 7:19 ` Ingo Molnar
2007-08-02 7:31 ` Nick Piggin
2007-08-02 15:44 ` Ingo Molnar
2007-08-03 0:14 ` Nick Piggin
2007-08-04 6:50 ` Ingo Molnar
2007-08-06 3:29 ` Nick Piggin
2007-08-13 12:30 ` Jens Axboe [this message]
2007-08-14 3:00 ` Andrew Morton
2007-08-14 3:23 ` Nick Piggin
2007-08-16 21:28 ` Siddha, Suresh B
2007-08-14 3:25 ` David Miller
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