Re: [tip:x86/idle] x86, hotplug: Move WBINVD back outside the play_dead loop

["H. Peter Anvin" <hpa@zytor.com>]

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?

	-hpa