Re: [PATCH v2] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR

[Ingo Molnar <mingo@kernel.org>]

* Uros Bizjak <ubizjak@gmail.com> wrote:

> There is another instance of the same sequence in arch/x86/kernel/smpboot.c:
> 
> 		/*
> 		 * The CLFLUSH is a workaround for erratum AAI65 for
> 		 * the Xeon 7400 series.  It's not clear it is actually
> 		 * needed, but it should be harmless in either case.
> 		 * The WBINVD is insufficient due to the spurious-wakeup
> 		 * case where we return around the loop.
> 		 */
> 		mb();
> 		clflush(md);
> 		mb();
> 		__monitor(md, 0, 0);
> 		mb();
> 		__mwait(eax_hint, 0);

True, but I wouldn't touch that - the shutdown path is not a 
performance critical code path in any fashion, and it's often
difficult to debug on real hardware, so the cost/benefit factor
is abnormally high.

Thanks,

	Ingo