linux-kernel - Re: [PATCH v3 2/2] cpufreq: add virtual-cpufreq driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZMjVKn1MwA2Avm7r@google.com>
Date:   Tue, 1 Aug 2023 09:49:30 +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

On Tuesday 01 Aug 2023 at 09:45:22 (+0000), Quentin Perret wrote:
> 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.

Alternatively we could make the schedutil margin configurable via the
cmdline or something along those lines, so we can set it to 0 in the
guest and avoid the issue entirely.

Some partners have been asking for this IIRC , so I suspect there would
be interest from other parties.

Thanks,
Quentin