Re: [PATCH] x86: Add clflush before monitor for Intel 7400 series

[H. Peter Anvin]

Venki Pallipadi wrote:
> For Intel 7400 series CPUs, the recommendation is to use a clflush on the
> monitored address just before monitor and mwait pair [1]. This clflush makes
> sure that there are no false wakeups from mwait when the monitored address
> was recently written to.
>
> [1] "MONITOR/MWAIT Recommendations for Intel Xeon Processor 7400 series"
> section in specification update document of 7400 series
> http://download.intel.com/design/xeon/specupdt/32033601.pdf
>
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>

This seems very expensive.  It really makes me wonder if it wouldn't 
just be better to either declare monitor/mwait non-functional on this 
chip, or make sure that mwaits can handle false wakeups.

	-hpa
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