From: Ionela Voinescu <ionela.voinescu@arm.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
linux-pm@vger.kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
Rafael Wysocki <rjw@rjwysocki.net>,
linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Sudeep Holla <sudeep.holla@arm.com>,
Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH V3 1/2] topology: Allow multiple entities to provide sched_freq_tick() callback
Date: Fri, 19 Feb 2021 09:44:40 +0000 [thread overview]
Message-ID: <20210219094440.GA29843@arm.com> (raw)
In-Reply-To: <20210219045823.beeijwaymd63prk7@vireshk-i7>
On Friday 19 Feb 2021 at 10:28:23 (+0530), Viresh Kumar wrote:
> On 18-02-21, 16:36, Ionela Voinescu wrote:
> > Yes, we don't care if there is no cpufreq driver, as the use of AMUs won't
> > get initialised either. But we do care if there is a cpufreq driver that
> > does not support frequency invariance, which is the example above.
> >
> > The intention with the patches that made cpufreq based invariance generic
> > a while back was for it to be present, seamlessly, for as many drivers as
> > possible, as a less than accurate invariance default method is still
> > better than nothing.
>
> Right.
>
> > So only a few drivers today don't support cpufreq based FI
>
> Only two AFAICT, both x86, and the AMU stuff doesn't conflict with
> them.
>
> drivers/cpufreq/intel_pstate.c
> drivers/cpufreq/longrun.c
>
> > but it's not a guarantee that it will stay this way.
>
> What do you mean by "no guarantee" here ?
>
> The very core routines (cpufreq_freq_transition_end() and
> cpufreq_driver_fast_switch()) of the cpufreq core call
> arch_set_freq_scale() today and this isn't going to change anytime
> soon. If something gets changed there someone will need to see other
> parts of the kernel which may get broken with that.
>
Yes, but it won't really be straightforward to notice this breakage if
that happens, so in my opinion it was worth to keep that condition.
> I don't see any need of complicating other parts of the kernel like,
> amu or cppc code for that. They should be kept simple and they should
> assume cpufreq invariance will be supported as it is today.
>
Fair enough! It is a corner case after all.
Thanks,
Ionela.
> --
> viresh
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next prev parent reply other threads:[~2021-02-19 9:45 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-28 10:48 [PATCH V3 0/2] cpufreq: cppc: Add support for frequency invariance Viresh Kumar
2021-01-28 10:48 ` [PATCH V3 1/2] topology: Allow multiple entities to provide sched_freq_tick() callback Viresh Kumar
2021-02-03 11:45 ` Ionela Voinescu
2021-02-05 9:14 ` Viresh Kumar
2021-02-17 0:24 ` Ionela Voinescu
2021-02-17 4:25 ` Viresh Kumar
2021-02-17 11:30 ` Ionela Voinescu
2021-02-17 11:40 ` Viresh Kumar
2021-02-17 11:57 ` Ionela Voinescu
2021-02-18 7:23 ` Viresh Kumar
2021-02-18 9:33 ` Viresh Kumar
2021-02-18 16:36 ` Ionela Voinescu
2021-02-19 4:58 ` Viresh Kumar
2021-02-19 9:44 ` Ionela Voinescu [this message]
2021-02-19 9:48 ` Viresh Kumar
2021-01-28 10:48 ` [PATCH V3 2/2] cpufreq: cppc: Add support for frequency invariance Viresh Kumar
2021-02-18 16:35 ` Ionela Voinescu
2021-02-22 11:00 ` Ionela Voinescu
2021-02-22 11:04 ` Viresh Kumar
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