Skylake: intel_pstate: fix PCT_TO_HWP macro

Zhang, Xiong Y xiong.y.zhang at intel.com
Fri Sep 25 01:25:30 UTC 2015


Hi, Xiaolong:
   Could you help me answer this ?

thanks
> -----Original Message-----
> From: Jason Gerard DeRose [mailto:jason at system76.com]
> Sent: Thursday, September 24, 2015 10:44 PM
> To: Zhang, Xiong Y; Ubuntu Kernel Team
> Subject: Re: Skylake: intel_pstate: fix PCT_TO_HWP macro
> 
> Thus far I've been testing this on SKL-S systems (one laptop, one
> desktop) and haven't experienced any system hangs.
> 
> Can you share any insight into the conditions under which these hangs
> occur, so I can try to reproduce it?
> 
> Also, when you say that hangs occur on "some SKL-S machines", are there
> any common denominators among the problematic machines? Or put another
> way, are there some SKL-S machines that are completely immune to these
> hangs, and if so, what's the difference?
> 
> Finally, an idea on the timeline for the complete fix?
> 
> Thanks!
> 
> On 09/23/2015 06:27 PM, Zhang, Xiong Y wrote:
> > 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!
> >>
> >> --
> >> kernel-team mailing list
> >> kernel-team at lists.ubuntu.com
> >> https://lists.ubuntu.com/mailman/listinfo/kernel-team




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