From: "H. Peter Anvin" <hpa@zytor.com>
To: Venkatesh Pallipadi <venki@google.com>
Cc: mingo@redhat.com, linux-kernel@vger.kernel.org,
asit.k.mallick@intel.com, arjan@linux.kernel.org,
a.p.zijlstra@chello.hl, lenb@kernel.org, tglx@linutronix.de,
hpa@linux.intel.com, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/idle] x86, hotplug: Move WBINVD back outside the play_dead loop
Date: Mon, 20 Sep 2010 11:20:31 -0700 [thread overview]
Message-ID: <4C97A5EF.4070100@zytor.com> (raw)
In-Reply-To: <AANLkTimCXZWVb7ajANPg15Zuo22nst=d5p-MjXhzu1NX@mail.gmail.com>
On 09/17/2010 05:48 PM, Venkatesh Pallipadi wrote:
>>
>> + wbinvd();
>> +
>> while (1) {
>> - mb();
>> - wbinvd();
>> __monitor(¤t_thread_info()->flags, 0, 0);
>> mb();
>
>
> Just one observation. There are some CPUs with errata that need
> clflush before monitor. So, if that CPU wakesup spuriously it may have
> problem reentering idle. Not sure whether that will be a problem as
> that errata also depended on read happening on the flag. May be its
> better to do monitor (0, 0, 0).
>
It seems the easy way to deal with that would be to just add clflush
before monitor... it is *probably* redundant, but it should be safe to
do. It means depending on X86_FEATURE_CLFLUSH as well as
X86_FEATURE_MWAIT, but I don't think there is any x86 processor which
has MWAIT and not CLFLUSH, and I highly doubt there ever will be.
Does anyone see any downside?
-hpa
next prev parent reply other threads:[~2010-09-20 18:22 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-22 23:19 [patch 0/2] x86: Make offline cpus to go to deepest idle state using mwait venkatesh.pallipadi
2009-05-22 23:19 ` [patch 1/2] x86: Add pm_play_dead funcptr to power-efficiently offline CPUs venkatesh.pallipadi
2009-05-23 10:44 ` Peter Zijlstra
2009-05-23 15:07 ` Pallipadi, Venkatesh
2009-06-22 17:25 ` Pallipadi, Venkatesh
2009-05-22 23:19 ` [patch 2/2] x86: put offline CPUs into deepest mwait cstate_subcstate venkatesh.pallipadi
2009-05-25 0:56 ` Shaohua Li
2009-05-26 21:17 ` Pallipadi, Venkatesh
2010-09-17 23:46 ` [tip:x86/idle] x86, hotplug: Use mwait to offline a processor, fix the legacy case tip-bot for H. Peter Anvin
2010-09-18 0:13 ` [tip:x86/idle] x86, hotplug: Move WBINVD back outside the play_dead loop tip-bot for H. Peter Anvin
2010-09-18 0:48 ` Venkatesh Pallipadi
2010-09-20 18:20 ` H. Peter Anvin [this message]
2010-09-20 20:11 ` H. Peter Anvin
2010-09-20 22:34 ` Venkatesh Pallipadi
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