Re: [tip:x86/urgent] x86 idle: Repair large-server 50-watt idle-power regression

[Davidlohr Bueso]

On Thu, 2013-12-19 at 11:51 -0800, tip-bot for Len Brown wrote:
> Commit-ID:  40e2d7f9b5dae048789c64672bf3027fbb663ffa
> Gitweb:     http://git.kernel.org/tip/40e2d7f9b5dae048789c64672bf3027fbb663ffa
> Author:     Len Brown <len.brown@xxxxxxxxx>
> AuthorDate: Wed, 18 Dec 2013 16:44:57 -0500
> Committer:  H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
> CommitDate: Thu, 19 Dec 2013 11:47:39 -0800
> 
> x86 idle: Repair large-server 50-watt idle-power regression

FYI this commit can cause some non trivial performance regressions for
larger core count systems. While not surprising because of the nature of
the change, having intel_idle do more cacheline invalidations, I still
wanted to let you guys know. For instance, on a 160 core Westmere
system, aim7 throughput can go down in a number of tests, anywhere from
-10% to -25%.

I guess it comes down to one of those performance vs energy things. And
sure, max_cstate can be set to overcome this, but it's still something
that was previously taken for granted.

Thanks,
Davidlohr

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