Skylake: intel_pstate: fix PCT_TO_HWP macro

Wang, Xiaolong xiaolong.wang at intel.com
Fri Sep 25 03:01:25 UTC 2015


Hi Jason,
We tested
  a SKL-S Beta machine
    (Processor Stepping in BIOS is Q0, F/M/S is 6/94/1), and
  a SKL-S Qual machine
    (Processor Stepping in BIOS is R0/S0, F/M/S is 6/94/3)
On the Beta machine, Processor Frequency are found tied at the highest
possible value -- HWP does not work;
On the Qual machine, it hangs just after HWP enabled on each core.

Upstream have reproduced the hang on a Beta machine (weird),
but they say removing "quiet" from boot parameters can boot to OS.
I tried removing "quiet" on my Qual machine, it didn't work.

As I know, upstream is still checking it but had not get the root cause
of that hang, and there is not a clear schedule to get that solved.

-Wang, Xiaolong

On 2015/9/25 9:25, Zhang, Xiong Y wrote:
> 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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