Re: 50 Watt idle power regression bisected to Linux-3.10

[Peter Zijlstra]

On Wed, Dec 11, 2013 at 03:42:38PM +0100, Ingo Molnar wrote:
> Another thing that is required I think is to issue a write barrier 
> before CLFLUSH instruction. By my (possibly incorrect ...) reading of 
> the documentation CLFLUSH does not appear to be ordered (at all), so 
> it might execute before the modification to the affected memory?
> 
> 
> So something like:
> 
>               if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) {
>                       smp_wmb(); /* order CLFLUSH */
>                       clflush(&current_thread_info()->flags);
>               }

smp_wmb() is a NO-OP on x86 remember :-)

Also, a wmb doesn't actually need to flush the store buffers.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/