From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Andi Kleen <ak@linux.intel.com>,
Mike Galbraith <bitbucket@online.de>,
Thomas Gleixner <tglx@linutronix.de>,
Frederic Weisbecker <fweisbec@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 0/7] preempt_count rework -v2
Date: Wed, 11 Sep 2013 09:00:30 -0700 [thread overview]
Message-ID: <5230939E.3050408@zytor.com> (raw)
In-Reply-To: <CA+55aFz3S6_g4TQ11VKGM3GW=a=r3qYWQ_a0qJ_5241qQz8D=w@mail.gmail.com>
On 09/10/2013 09:24 AM, Linus Torvalds wrote:
> On Tue, Sep 10, 2013 at 8:29 AM, Arjan van de Ven <arjan@linux.intel.com> wrote:
>>>
>> also.. yuck on using "dec"
>> "dec" sucks, please use "sub foo ,1" instead
>
> That's a bigger instruction, largely due to the constant.
>
>> (dec sucks because of its broken flags behavior; it creates basically a
>> bubble in the pipeline)
>
> Intel could (and should) just fix that. It's "easy" enough - you just
> need to rename the carry flag as a separate register (and make sure
> that the conditional instructions that don't use it don't think they
> need it).
>
> In fact I thought Intel already did that on their large cores. Are you
> sure they still have trouble with inc/dec?
>
Big cores are fine, but Atom (and presumably Quark) might still suffer a
performance penalty.
-hpa
next prev parent reply other threads:[~2013-09-11 16:01 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-10 13:08 Peter Zijlstra
2013-09-10 13:08 ` [PATCH 1/7] sched: Introduce preempt_count accessor functions Peter Zijlstra
2013-09-10 13:08 ` [PATCH 2/7] sched: Add NEED_RESCHED to the preempt_count Peter Zijlstra
2013-09-11 1:59 ` Andy Lutomirski
2013-09-11 8:25 ` Peter Zijlstra
2013-09-11 11:06 ` Peter Zijlstra
2013-09-11 13:34 ` Mike Galbraith
2013-09-12 6:01 ` Mike Galbraith
2013-09-11 16:35 ` Andy Lutomirski
2013-09-11 18:05 ` Peter Zijlstra
2013-09-11 18:07 ` Andy Lutomirski
2013-09-11 11:14 ` Peter Zijlstra
2013-09-10 13:08 ` [PATCH 3/7] sched, arch: Create asm/preempt.h Peter Zijlstra
2013-09-10 13:08 ` [PATCH 4/7] sched: Create more preempt_count accessors Peter Zijlstra
2013-09-10 13:08 ` [PATCH 5/7] sched: Extract the basic add/sub preempt_count modifiers Peter Zijlstra
2013-09-10 13:08 ` [PATCH 6/7] sched, x86: Provide a per-cpu preempt_count implementation Peter Zijlstra
2013-09-10 13:27 ` Peter Zijlstra
2013-09-10 14:02 ` Eric Dumazet
2013-09-10 15:25 ` Peter Zijlstra
2013-09-10 16:48 ` Peter Zijlstra
2013-09-10 13:08 ` [PATCH 7/7] sched, x86: Optimize the preempt_schedule() call Peter Zijlstra
2013-09-10 13:42 ` Ingo Molnar
2013-09-10 13:55 ` Jan Beulich
2013-09-10 14:25 ` Ingo Molnar
2013-09-10 13:51 ` [PATCH 0/7] preempt_count rework -v2 Ingo Molnar
2013-09-10 13:56 ` Ingo Molnar
2013-09-10 15:14 ` Peter Zijlstra
2013-09-10 15:29 ` Arjan van de Ven
2013-09-10 15:35 ` Peter Zijlstra
2013-09-10 16:24 ` Linus Torvalds
2013-09-11 16:00 ` H. Peter Anvin [this message]
2013-09-10 16:34 ` Linus Torvalds
2013-09-10 16:45 ` Peter Zijlstra
2013-09-10 17:06 ` Linus Torvalds
2013-09-10 21:25 ` Peter Zijlstra
2013-09-10 21:43 ` Linus Torvalds
2013-09-10 21:51 ` H. Peter Anvin
2013-09-10 22:02 ` Linus Torvalds
2013-09-10 22:06 ` H. Peter Anvin
2013-09-11 13:13 ` Peter Zijlstra
2013-09-11 13:26 ` Peter Zijlstra
2013-09-11 15:29 ` H. Peter Anvin
2013-09-11 15:33 ` Linus Torvalds
2013-09-11 18:59 ` Peter Zijlstra
2013-09-11 23:02 ` Linus Torvalds
2013-09-12 2:20 ` Peter Zijlstra
2013-09-12 2:43 ` Linus Torvalds
2013-09-12 11:51 ` Peter Zijlstra
2013-09-12 12:25 ` Ingo Molnar
2013-09-13 7:25 ` Kevin Easton
2013-09-13 8:06 ` Peter Zijlstra
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