From: Andi Kleen <ak@suse.de>
To: Benjamin LaHaise <bcrl@kvack.org>
Cc: Linus Torvalds <torvalds@osdl.org>, Andrew Morton <akpm@osdl.org>,
Chuck Ebbert <76306.1226@compuserve.com>,
In Cognito <defend.the.world@gmail.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: Sysenter crash with Nested Task Bit set
Date: Mon, 18 Sep 2006 18:39:45 +0200 [thread overview]
Message-ID: <200609181839.45546.ak@suse.de> (raw)
In-Reply-To: <20060918161251.GC19815@kvack.org>
On Monday 18 September 2006 18:12, Benjamin LaHaise wrote:
> On Mon, Sep 18, 2006 at 05:29:23PM +0200, Andi Kleen wrote:
> > > - asm volatile("pushl %%ebp\n\t" \
> > > + asm volatile("pushfl\n\t" /* Save flags */ \
> > > + "pushl %%ebp\n\t" \
> >
> > We used to do that pushfl/popfl some time ago, but Ben removed it because
> > it was slow on P4. Ok, nobody thought of that case back then.
>
> It's the pushfl that will be slow on any OoO CPU, as it has dependancies on
> any previous instructions that modified the flags, which ends up bringing
> all of the memory ordering dependancies into play. Doing a popfl to set the
> flags to some known value is much less expensive.
Yes it's never fast, but on basically all non P4 CPUs it is still fast enough
to not be a problem. I suppose it causes a trace cache flush or something like
that there.
-Andi
next prev parent reply other threads:[~2006-09-18 16:50 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-18 3:51 Sysenter crash with Nested Task Bit set Chuck Ebbert
2006-09-18 5:25 ` Andrew Morton
2006-09-18 8:44 ` Mike Galbraith
2006-09-18 15:11 ` Linus Torvalds
2006-09-18 15:06 ` Ingo Molnar
2006-09-18 15:29 ` Andi Kleen
2006-09-18 15:24 ` Ingo Molnar
2006-09-18 16:02 ` Linus Torvalds
2006-09-18 16:10 ` Linus Torvalds
2006-09-18 16:24 ` Jeremy Fitzhardinge
2006-09-18 16:12 ` Benjamin LaHaise
2006-09-18 16:39 ` Andi Kleen [this message]
2006-09-18 19:01 ` Jeremy Fitzhardinge
[not found] <5a20704e0609171603s55ca52bap71dc2fa2c05d6741@mail.gmail.com>
2006-09-17 23:08 ` In Cognito
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