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SubjectRE: [PATCH][v5] x86, suspend: Save/restore extra MSR registers for suspend
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Hi, Boris,

> -----Original Message-----
> From: Borislav Petkov [mailto:bp@suse.de]
> Sent: Tuesday, October 13, 2015 12:38 AM
> To: Chen, Yu C
> Cc: mingo@redhat.com; rjw@rjwysocki.net; pavel@ucw.cz;
> tglx@linutronix.de; hpa@zytor.com; Zhang, Rui; luto@kernel.org;
> linux@horizon.com; dsmythies@telus.net; linux-pm@vger.kernel.org;
> x86@kernel.org; linux-kernel@vger.kernel.org; Kaszewski, Marcin
> Subject: Re: [PATCH][v5] x86, suspend: Save/restore extra MSR registers for
> suspend
>
> On Sun, Oct 11, 2015 at 11:20:01AM +0800, Chen Yu wrote:
> > A bug is reported(https://bugzilla.redhat.com/show_bug.cgi?id=1227208)
>
> I get:
>
> "You are not authorized to access bug #1227208.
>
> Most likely the bug has been restricted for internal development processes
> and we cannot grant access."
>
> > that, after resumed from S3, CPU is running at a low speed.
> > After investigation, it is found that, BIOS has modified the value of
> > THERM_CONTROL register during S3, and changes it from 0 to 0x10 (thus
> > changes the clock modulation from reserved to enabled), since value of
> > 0x10 means CPU can only get 25% of the Duty Cycle, this triggers the
> > problem.
>
> Is this what the bug described above is? In any case, please remove the
> private bugzilla link and describe the bug in text here.
Yes, this bug is described in the changelog, I'll remove the link.
>
> Also, from reading the other thread about the v4 patch, it sounds like
> intel_pstate can't handle the clock modulation properly, according to what
> Doug says.
As discussed with Doug in the v4 patch, the problem brought by clock modulation
is because intel_pstate use a theoretical pstate to calculate the cpu busy ratio,
and Doug has proposed a patch to use compensatory algorithm in intel_pstate,
to predict the pstate based on actual cpu freq(take clock modulation into account),
which can fix his problem now.
So I'll resend a version 6 of current patch, because some server in production
environment has suffered from this problem for some time.. thanks.

Best regards,
Yu
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