Re: [PATCH v5 6/7] cpufreq: amd-pstate: update pstate frequency transition delay time

Punit Agrawal
2022-08-16T16:05:37Z

Hi Perry,

"Yuan, Perry" <Perry.Yuan@amd.com> writes:

> [AMD Official Use Only - General]
>
> Hi Punit
>
>> -----Original Message-----
>> From: Punit Agrawal <punit.agrawal@bytedance.com>
>> Sent: Monday, August 15, 2022 11:06 PM
>> To: Yuan, Perry <Perry.Yuan@amd.com>
>> Cc: rafael.j.wysocki@intel.com; Huang, Ray <Ray.Huang@amd.com>;
>> viresh.kumar@linaro.org; Sharma, Deepak <Deepak.Sharma@amd.com>;
>> Limonciello, Mario <Mario.Limonciello@amd.com>; Fontenot, Nathan
>> <Nathan.Fontenot@amd.com>; Deucher, Alexander
>> <Alexander.Deucher@amd.com>; Su, Jinzhou (Joe) <Jinzhou.Su@amd.com>;
>> Huang, Shimmer <Shimmer.Huang@amd.com>; Du, Xiaojian
>> <Xiaojian.Du@amd.com>; Meng, Li (Jassmine) <Li.Meng@amd.com>; linux-
>> pm@vger.kernel.org; linux-kernel@vger.kernel.org
>> Subject: Re: [PATCH v5 6/7] cpufreq: amd-pstate: update pstate frequency
>> transition delay time
>>
>> [CAUTION: External Email]
>>
>> Perry Yuan <Perry.Yuan@amd.com> writes:
>>
>> > Change the default transition latency to be 20ms that is more
>> > reasonable transition delay for AMD processors in non-EPP driver mode.
>> >
>> > Update transition delay time to 1ms, in the AMD CPU autonomous mode
>> > and non-autonomous mode, CPPC firmware will decide frequency at 1ms
>> > timescale based on the workload utilization.
>> >
>> > Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
>> > Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
>> > ---
>> > drivers/cpufreq/amd-pstate.c | 4 ++--
>> > 1 file changed, 2 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/cpufreq/amd-pstate.c
>> > b/drivers/cpufreq/amd-pstate.c index e40177d14310..9cb051d61422 100644
>> > --- a/drivers/cpufreq/amd-pstate.c
>> > +++ b/drivers/cpufreq/amd-pstate.c
>> > @@ -41,8 +41,8 @@
>> > #include <asm/msr.h>
>> > #include "amd-pstate-trace.h"
>> >
>> > -#define AMD_PSTATE_TRANSITION_LATENCY 0x20000
>> > -#define AMD_PSTATE_TRANSITION_DELAY 500
>> > +#define AMD_PSTATE_TRANSITION_LATENCY 20000
>> > +#define AMD_PSTATE_TRANSITION_DELAY 1000
>>
>> How were these values derived? If from documentation, it'll be good to add a
>> link to the relevant documentation. And if they were derived from testing,
>> please mention this in the commit log (along with some details of the tests used
>> to determine the value).
>
> The values are calculated from the CPU PM firmware and hardware design.
> There are some latency and delay values defined in the PM firmware, I have no documents about the detail for now.

In that case, please mention that the values are calculated from
firmware / hardware design in the commit log (and include a reference to
the firmware sources if available).

Thanks! …