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Message-ID: <ZMjUMk5xXzahXjno@google.com>
Date: Tue, 1 Aug 2023 09:45:22 +0000
From: Quentin Perret <qperret@...gle.com>
To: David Dai <davidai@...gle.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Conor Dooley <conor+dt@...nel.org>,
Sudeep Holla <sudeep.holla@....com>,
Saravana Kannan <saravanak@...gle.com>,
Masami Hiramatsu <mhiramat@...gle.com>,
Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Marc Zyngier <maz@...nel.org>,
Oliver Upton <oliver.upton@...ux.dev>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Pavan Kondeti <quic_pkondeti@...cinc.com>,
Gupta Pankaj <pankaj.gupta@....com>,
Mel Gorman <mgorman@...e.de>, kernel-team@...roid.com,
linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] cpufreq: add virtual-cpufreq driver
Hi David,
On Monday 31 Jul 2023 at 10:46:09 (-0700), David Dai wrote:
> +static unsigned int virt_cpufreq_set_perf(struct cpufreq_policy *policy)
> +{
> + struct virt_cpufreq_drv_data *data = policy->driver_data;
> + /*
> + * Use cached frequency to avoid rounding to freq table entries
> + * and undo 25% frequency boost applied by schedutil.
> + */
The VMM would be a better place for this scaling I think, the driver
can't/shouldn't make assumptions about the governor it is running with
given that this is a guest userspace decision essentially.
IIRC the fast_switch() path is only used by schedutil, so one could
probably make a case to scale things there, but it'd be inconsistent
with the "slow" switch case, and would create a fragile dependency, so
it's probably not worth pursuing.
> + u32 freq = mult_frac(policy->cached_target_freq, 80, 100);
> +
> + data->ops->set_freq(policy, freq);
> + return 0;
> +}
Thanks,
Quentin
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