[U-Boot] [PATCH v2 1/2] x86: TunnelCreek: switch P state to the highest freq

[Bin Meng]

Hi Christian,

On Wed, Mar 13, 2019 at 5:27 PM Christian Gmeiner
<christian.gmeiner at gmail.com> wrote:
>
> Hi all,
>
> Am Mo., 11. März 2019 um 15:41 Uhr schrieb Bin Meng <bmeng.cn at gmail.com>:
> >
> > Hi Andy,
> >
> > On Wed, Mar 6, 2019 at 7:09 PM Andy Shevchenko
> > <andriy.shevchenko at linux.intel.com> wrote:
> > >
> > > On Thu, Feb 28, 2019 at 11:29:50AM +0800, Bin Meng wrote:
> > > > On Thu, May 24, 2018 at 12:00 PM Bin Meng <bmeng.cn at gmail.com> wrote:
> > > > > On Thu, Apr 12, 2018 at 4:07 PM, Christian Gmeiner
> > > > > <christian.gmeiner at gmail.com> wrote:
> > >
> > > > So to me this seems to match my understanding about EIST. If this is
> > > > true, then I can't explain why Christian's patch is needed since the
> > > > EIST is disabled on TunnelCreek by default and the processor should
> > > > already run at the highest performance.
> > >
> > > The some internal documents I found suggesting that first what one needs to do
> > > is to be sure that EIST is enabled / disabled by reading a bit from CPUID.
> > >
> >
> > Correct. This is documented in the public Intel SDM too.
> >
> > > (There is no mention of the exact bit, I'm guessing it might be X86_FEATURE_EST)
> > >
> > > It also refers to IA32_MISC_ENABLE MSR, i.e. bit 20
> > > (MSR_IA32_MISC_ENABLE_SPEEDSTEP_LOCK_BIT) and bit 16
> > > (MSR_IA32_MISC_ENABLE_ENHANCED_SPEEDSTEP_BIT), that firmware can set up
> > > accordingly.
> > >
> > > Hope this helps.
> > >
> >
> > Thanks for the help. But I was looking for clarification on what
> > frequency the CPU is running at if EIST is disabled (the default
> > power-up state). Especially I suspect the Intel CPU is running at the
> > highest frequency when ESIT is disabled hence the highest performance.
> > Such details are not documented in the public Intel SDM. :(
> >
> > > P.S. All names are implying Linux kernel source code.
> >
>
> I think I need to clarify how I came to this patch.
>
> Back in the days when we used an Intel BLDK based BIOS solution we did
> some performance
> measurements and found out that the same device with an vendor BIOS is
> much faster. So we started
> to dig into the issue and used bandwidth to do our measurements. We
> contacted Intel to get support
> and after lot of ping-pong mails we got a solution.
>
> We need to set these two msr registers to the values they provided to us.
> These msr register should be described in #29324.

Could you please provide details about these 2 MSR registers? And is
there any official document from Intel about what is the behavior of
having EIST disabled?

>
> Bin do you have hardware to reproduce this issue I have and what gets
> fixed with this patch?

Yes, I have the hardware to test. Is the test case able to run in
U-Boot? I can have a test.

Regards,
Bin