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From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Huang Rui <ray.huang@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Borislav Petkov <bp@suse.de>, Ingo Molnar <mingo@kernel.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"Sharma, Deepak" <Deepak.Sharma@amd.com>,
	"Deucher, Alexander" <Alexander.Deucher@amd.com>,
	"Limonciello, Mario" <Mario.Limonciello@amd.com>,
	"Fontenot, Nathan" <Nathan.Fontenot@amd.com>,
	"Su, Jinzhou (Joe)" <Jinzhou.Su@amd.com>,
	"Du, Xiaojian" <Xiaojian.Du@amd.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>
Subject: Re: [PATCH 04/19] cpufreq: amd: introduce a new amd pstate driver to support future processors
Date: Thu, 16 Sep 2021 13:19:21 +0200	[thread overview]
Message-ID: <CAJZ5v0i7OHBmQL-WdaiBsYaO2J6kCqW=YzA8jU6nQBJ2nw0JQQ@mail.gmail.com> (raw)
In-Reply-To: <20210916100947.GE3755511@hr-amd>

On Thu, Sep 16, 2021 at 12:09 PM Huang Rui <ray.huang@amd.com> wrote:
>
> On Mon, Sep 13, 2021 at 07:56:32PM +0800, Peter Zijlstra wrote:
> > On Mon, Sep 13, 2021 at 06:54:58PM +0800, Huang Rui wrote:
> > > On Mon, Sep 13, 2021 at 04:56:24PM +0800, Peter Zijlstra wrote:
> >
> > > > > 1) Full MSR Support
> > > > > If current hardware has the full MSR support, we register "pstate_funcs"
> > > > > callback functions to implement the MSR operations to control the clocks.
> > > >
> > > > What's the WRMSR cost for those? I've not really kept track of the MSR
> > > > costs on AMD platforms, but on Intel it has (luckily) been coming down
> > > > quite a bit.
> > >
> > > Good to know this, I didn't have a chance to give a check. May I know how
> > > did you test this latency? But MSR is new hardware design for this
> > > solution, as designer mentioned, the WRMSR is low-latency register model is
> > > faster than ACPI AML code interpreter.
> > >
> > > >
> > > > > 2) Shared Memory Support
> > > > > If current hardware doesn't have the full MSR support, that means it only
> > > > > provides share memory support. We will leverage APIs in cppc_acpi libs with
> > > > > "cppc_funcs" to implement the target function for the frequency control.
> > > >
> > > > Right, the mailbox thing. How is the performance of this vs MSR accesses?
> > >
> > > I will give a check. If you have a existing test method that can be used, I
> > > can check it quickly.
> >
> > Oh, I was mostly wondering if using the mailbox as MMIO would be faster
> > than an MSR, but you've already answered that above. Also:
> >
> > > > > 1. As mentioned above, amd-pstate driver can implement
> > > > > fast_switch/adjust_perf function with full MSR operations that have better
> > > > > performance for schedutil and other governors.
> > > >
> > > > Why couldn't the existing cppc-cpufreq grow this?
> > >
> > > Because fast_switch can adjust the frequency directly in the interrupt
> > > context, if we use the acpi cppc handling with shared memory solution, it
> > > will have a deadlock. So fast switch needs the control with registers
> > > directly like acpi-cpufreq and intel-pstate.
> >
> > Aah, I see, you're only doing fast_switch support when you have MSRs.
> > That was totally non-obvious.. :/
>
> Yes, I should have written a comment to there. :-)
> Will update this in V2.
>
> >
> > But then amd_pstate_adjust_perf() could just direct call the pstate
> > methods and we don't need that indirection *at*all*, right?
>
> Hmm, yes, if we use amd_pstate_adjust_perf here, we won't need to call
> amd_pstate_fast_switch. I saw intel_pstate had adjust_perf and fast_switch
> at the same time, would you mind to let me know how to distinguish these
> two use scenario on intel processors?

The ->fast_switch() callback is for the use cases in which
->adjust_perf() cannot be installed, that is basically systems without
HWP enabled.

  reply	other threads:[~2021-09-16 11:19 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-08 14:59 [PATCH 00/19] cpufreq: introduce a new AMD CPU frequency control mechanism Huang Rui
2021-09-08 14:59 ` [PATCH 01/19] x86/cpufreatures: add AMD CPPC extension feature flag Huang Rui
2021-09-08 20:00   ` Shuah Khan
2021-09-09  9:45     ` Huang Rui
2021-09-09 17:58   ` Borislav Petkov
2021-09-13  9:48     ` Huang Rui
2021-09-13 13:04       ` Borislav Petkov
2021-09-16  9:30         ` Huang Rui
2021-09-08 14:59 ` [PATCH 02/19] x86/msr: add AMD CPPC MSR definitions Huang Rui
2021-09-08 14:59 ` [PATCH 03/19] ACPI: CPPC: add cppc enable register function Huang Rui
2021-09-08 19:14   ` Fontenot, Nathan
2021-09-09  9:50     ` Huang Rui
2021-09-09  0:21   ` Shuah Khan
2021-09-09  9:58     ` Huang Rui
2021-09-08 14:59 ` [PATCH 04/19] cpufreq: amd: introduce a new amd pstate driver to support future processors Huang Rui
2021-09-09 15:01   ` Peter Zijlstra
2021-09-13  8:11     ` Huang Rui
2021-09-13  8:56       ` Peter Zijlstra
2021-09-13 10:54         ` Huang Rui
2021-09-13 11:56           ` Peter Zijlstra
2021-09-16 10:09             ` Huang Rui
2021-09-16 11:19               ` Rafael J. Wysocki [this message]
2021-09-17  3:41                 ` Huang Rui
2021-09-09 15:03   ` Peter Zijlstra
2021-09-13 11:55     ` Huang Rui
2021-09-09 19:31   ` Fontenot, Nathan
2021-09-13 11:18     ` Huang Rui
2021-09-08 14:59 ` [PATCH 05/19] cpufreq: amd: add fast switch function for amd-pstate module Huang Rui
2021-09-08 14:59 ` [PATCH 06/19] cpufreq: amd: add acpi cppc function as the backend for legacy processors Huang Rui
2021-09-08 14:59 ` [PATCH 07/19] cpufreq: amd: add trace for amd-pstate module Huang Rui
2021-09-08 14:59 ` [PATCH 08/19] cpufreq: amd: add boost mode support for amd-pstate Huang Rui
2021-09-08 18:24   ` Fontenot, Nathan
2021-09-09 10:12     ` Huang Rui
2021-09-08 14:59 ` [PATCH 09/19] cpufreq: amd: add amd-pstate checking support check attribute Huang Rui
2021-09-08 14:59 ` [PATCH 10/19] cpufreq: amd: add amd-pstate frequencies attributes Huang Rui
2021-09-08 18:13   ` Fontenot, Nathan
2021-09-08 14:59 ` [PATCH 11/19] cpufreq: amd: add amd-pstate performance attributes Huang Rui
2021-09-08 18:20   ` Fontenot, Nathan
2021-09-08 14:59 ` [PATCH 12/19] cpupower: add AMD P-state capability flag Huang Rui
2021-09-08 14:59 ` [PATCH 13/19] cpupower: add the function to check amd-pstate enabled Huang Rui
2021-09-09 22:16   ` Shuah Khan
2021-09-13 11:29     ` Huang Rui
2021-09-08 14:59 ` [PATCH 14/19] cpupower: initial AMD P-state capability Huang Rui
2021-09-09 22:16   ` Shuah Khan
2021-09-13 12:58     ` Huang Rui
2021-09-08 14:59 ` [PATCH 15/19] cpupower: add amd-pstate sysfs entries into libcpufreq Huang Rui
2021-09-09 22:26   ` Shuah Khan
2021-09-16  8:47     ` Huang Rui
2021-09-08 14:59 ` [PATCH 16/19] cpupower: enable boost state support for amd-pstate module Huang Rui
2021-09-08 17:32   ` Fontenot, Nathan
2021-09-09  9:59     ` Huang Rui
2021-09-09 22:42   ` Shuah Khan
2021-09-16  9:27     ` Huang Rui
2021-09-08 14:59 ` [PATCH 17/19] cpupower: add amd-pstate get data function to query the info Huang Rui
2021-09-09 22:45   ` Shuah Khan
2021-09-08 15:00 ` [PATCH 18/19] cpupower: print amd-pstate information on cpupower Huang Rui
2021-09-09 22:46   ` Shuah Khan
2021-09-16  9:29     ` Huang Rui
2021-09-08 15:00 ` [PATCH 19/19] Documentation: amd-pstate: add amd-pstate driver introduction Huang Rui

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