From: Ionela Voinescu <ionela.voinescu@arm.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V3 3/3] arm64: topology: Make AMUs work with modular cpufreq drivers
Date: Fri, 8 Jan 2021 09:44:17 +0000 [thread overview]
Message-ID: <20210108094416.GA19952@arm.com> (raw)
In-Reply-To: <20201217105049.z3aqhl4mo56hhqvk@vireshk-i7>
On Thursday 17 Dec 2020 at 16:20:49 (+0530), Viresh Kumar wrote:
> On 16-12-20, 19:37, Ionela Voinescu wrote:
> > I did not yet test this, but reading this comment made me wonder..
> >
> > arch_scale_freq_invariant() (or topology_scale_freq_invariant()) is also
> > called from schedutil when obtaining the next frequency.
> >
> > So if we had a system that only partly supports AMUs but had at some
> > point a cpufreq driver that provided FIE for the other CPUs, when we
> > unregister the driver, the cpufreq_freq_invariance static key is
> > disabled. Therefore, none of the conditions for system invariance is
> > now accomplished and arch_scale_freq_invariant() will return false.
> > This will be broken as utilization is still scaled, but the algorithm
> > for computing the next frequency in schedutil will not take this into
> > account.
>
> I think the best and the easiest solution for this is:
>
> bool arch_freq_counters_available(const struct cpumask *cpus)
> {
> return amu_freq_invariant();
> }
>
> But we probably need to rename it to something like arch_is_fie().
>
Now that I think of it again (after spending 30 minutes trying to come
up with a more clear solution) I realised this is not actually a
problem :).
The only location that checks the invariance status is schedutil, but
what a cpufreq governor does becomes irrelevant if you remove the
cpufreq driver. The only potential problem is if one then inmods a
cpufreq driver that's not invariant. But I think that might be on "if"
too many to consider. What do you think?
Thanks,
Ionela.
next prev parent reply other threads:[~2021-01-08 9:45 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 5:34 [PATCH V3 1/3] arm64: topology: Avoid the have_policy check Viresh Kumar
2020-12-15 5:34 ` [PATCH V3 2/3] arm64: topology: Reorder init_amu_fie() a bit Viresh Kumar
2020-12-15 11:53 ` Ionela Voinescu
2020-12-15 5:34 ` [PATCH V3 3/3] arm64: topology: Make AMUs work with modular cpufreq drivers Viresh Kumar
2020-12-15 11:56 ` Ionela Voinescu
2020-12-16 0:03 ` Ionela Voinescu
2020-12-16 4:38 ` Viresh Kumar
2020-12-16 19:37 ` Ionela Voinescu
2020-12-17 10:50 ` Viresh Kumar
2021-01-08 9:44 ` Ionela Voinescu [this message]
2021-01-08 10:42 ` Ionela Voinescu
2021-01-08 11:03 ` Viresh Kumar
2020-12-17 7:57 ` [PATCH V3 1/3] arm64: topology: Avoid the have_policy check Viresh Kumar
2020-12-17 10:55 ` Catalin Marinas
2020-12-18 4:26 ` Viresh Kumar
2020-12-18 11:01 ` Catalin Marinas
2020-12-18 11:04 ` Viresh Kumar
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