Skylake: intel_pstate: fix PCT_TO_HWP macro

Zhang, Xiong Y xiong.y.zhang at intel.com
Thu Sep 24 00:27:38 UTC 2015


Yes, this patch will resolve p states on SKL-Y and SKL-U, but it also generate system hang on some SKL-S machines. We are still waiting extra patches to fix it.

thanks
> -----Original Message-----
> From: kernel-team-bounces at lists.ubuntu.com
> [mailto:kernel-team-bounces at lists.ubuntu.com] On Behalf Of Jason Gerard
> DeRose
> Sent: Thursday, September 24, 2015 2:52 AM
> To: Ubuntu Kernel Team
> Subject: Skylake: intel_pstate: fix PCT_TO_HWP macro
> 
> I think commit 74da56ce5c6715630aed3ccc0fcb86a9210c1a56 is very worthy
> of cherry-picking before the kernel freeze.
> 
>  From the bug I just filed:
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1499040
> 
> The intel pstate driver is currently quite broken on on Skylake hardware.
> 
> The symptom is that the pstate driver can scale the frequency up, but
> wont then scale it back down. So as soon as you hit a decent amount of
> CPU load, you get stuck fluctuating in the turbo frequency ranges, never
> even dropping as low as the base clock frequency. Obviously this has
> very negative consequences for battery life.
> 
> Commit 74da56ce5c6715630aed3ccc0fcb86a9210c1a56 fixes this upstream,
> which is included in 4.3rc2:
> 
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=74d
> a56ce5c6715630aed3ccc0fcb86a9210c1a56
> 
> I built a custom Ubuntu kernel with this commit and tested it on a
> laptop with a Skylake i7-6700 CPU. As measured by powerstat, this commit
> dropped the idle power consumption by 11 watts (from 34 to 23 watts,
> screen backlight was off during the test).
> 
> I also tested this custom kernel on Haswell and Ivy Bridge hardware to
> make sure it didn't introduce any behaviour changes in the pstate driver
> on older hardware. As far as I can tell, on this older hardware pstate
> is behaving exactly the same with and without this commit.
> 
> Thanks!
> 
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