Skylake: intel_pstate: fix PCT_TO_HWP macro

Jason Gerard DeRose jason at system76.com
Fri Sep 25 16:09:49 UTC 2015


Wang,

On 09/24/2015 09:01 PM, Wang, Xiaolong wrote:
> 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.

Thanks for sharing these insights.

> 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.

Yeah, I'd be kinda doubtful that "quiet" would have any effect either 
way, but I guess weirder things have happened :)

> 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.

Thank for the info!
-Jason

> -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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