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SubjectRe: [tip:x86/idle] x86, hotplug: Move WBINVD back outside the play_dead loop
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On Mon, Sep 20, 2010 at 1:11 PM, H. Peter Anvin <hpa@zytor.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@google.com>
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