linux-kernel - Re: [tip:x86/idle] x86, hotplug: Move WBINVD back outside the play

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Message-ID: <AANLkTikJGJ_84fbtVTqGv-zsJUKUQBQO2ZG6tKQnzFCf@mail.gmail.com>
Date:	Mon, 20 Sep 2010 15:34:02 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	asit.k.mallick@...el.com, arjan@...ux.kernel.org,
	a.p.zijlstra@...llo.hl, lenb@...nel.org, tglx@...utronix.de,
	hpa@...ux.intel.com, linux-tip-commits@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [tip:x86/idle] x86, hotplug: Move WBINVD back outside the
 play_dead loop

On Mon, Sep 20, 2010 at 1:11 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 09/20/2010 11:20 AM, H. Peter Anvin wrote:
>> On 09/17/2010 05:48 PM, Venkatesh Pallipadi wrote:
>>>>
>>>> +       wbinvd();
>>>> +
>>>>        while (1) {
>>>> -               mb();
>>>> -               wbinvd();
>>>>                __monitor(&current_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?
>>
>
> Patch for review... anyone see any problem with it?
>

Looks good.

We can also close one of the longest standing bugs in
bugzilla.kernel.org  now :-)
https://bugzilla.kernel.org/show_bug.cgi?id=5471

Acked-by: Venkatesh Pallipadi <venki@...gle.com>
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