From: "H. Peter Anvin" <hpa@zytor.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Len Brown <lenb@kernel.org>,
x86@kernel.org, linux-pm@vger.kernel.org,
linux-kernel@vger.kernel.org, Len Brown <len.brown@intel.com>,
stable@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Mike Galbraith <efault@gmx.de>, Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH] x86 idle: repair large-server 50-watt idle-power regression
Date: Thu, 19 Dec 2013 10:19:22 -0800 [thread overview]
Message-ID: <52B338AA.1020307@zytor.com> (raw)
In-Reply-To: <52B33640.3020204@zytor.com>
On 12/19/2013 10:09 AM, H. Peter Anvin wrote:
> On 12/19/2013 09:07 AM, Ingo Molnar wrote:
>>
>> Likewise, having a barrier before the MONITOR looks sensible as well.
>> Having it _after_ monitor looks weird and is probably wrong. [It might
>> have been the effects of someone seeing the spurious wakeup problems
>> with realizing the true source, or so.]
>>
>
> Does anyone know the history of this barrier after the monitor? I know
> Len is looking for a minimal patchset that can go into -stable, and it
> seems prudent to not preturb the code more than necessary, but going
> forward it would be nice to know...
>
Hmm... it *looks* like it is intended to be part of the construct:
smp_mb();
if (!need_resched())
...
I found a note in the HLT variant of the function saying:
/*
* TS_POLLING-cleared state must be visible before we
* test NEED_RESCHED:
*/
... which presumably has been copied elsewhere.
-hpa
next prev parent reply other threads:[~2013-12-19 18:19 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-18 21:44 [PATCH] x86 idle: repair large-server 50-watt idle-power regression Len Brown
2013-12-19 12:22 ` Ingo Molnar
2013-12-19 14:40 ` H. Peter Anvin
2013-12-19 15:45 ` Borislav Petkov
2013-12-19 15:55 ` H. Peter Anvin
2013-12-19 16:02 ` Ingo Molnar
2013-12-19 16:09 ` H. Peter Anvin
2013-12-19 16:13 ` H. Peter Anvin
2013-12-19 16:21 ` Peter Zijlstra
2013-12-19 16:50 ` H. Peter Anvin
2013-12-19 17:07 ` Ingo Molnar
2013-12-19 17:25 ` Peter Zijlstra
2013-12-19 17:36 ` Peter Zijlstra
2013-12-19 18:05 ` H. Peter Anvin
2013-12-19 18:14 ` Ingo Molnar
2013-12-19 17:50 ` Peter Zijlstra
2013-12-19 18:18 ` Ingo Molnar
2013-12-19 21:05 ` H. Peter Anvin
2013-12-19 21:17 ` Ingo Molnar
2013-12-19 18:10 ` Ingo Molnar
2013-12-19 18:09 ` H. Peter Anvin
2013-12-19 18:19 ` H. Peter Anvin [this message]
2013-12-19 18:23 ` Ingo Molnar
[not found] ` <CA+55aFzGxcML7j8CEvQPYzh0W81uVoAAVmGctMOUZ7CZ1yYd2A@mail.gmail.com>
2013-12-19 18:43 ` Ingo Molnar
2013-12-19 18:19 ` Ingo Molnar
2013-12-19 19:22 ` H. Peter Anvin
2013-12-19 19:27 ` Peter Zijlstra
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