linux-kernel - Re: [PATCH v7 0/2] Improve VM CPUfreq and task placement behavior

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Message-ID: <CAGETcx-dYERAbW4mTrSFi9j6wt1OQ3UKyxHiw-+40_VoKSdxag@mail.gmail.com>
Date: Mon, 28 Oct 2024 13:48:46 -0700
From: Saravana Kannan <saravanak@...gle.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>, David Dai <davidai@...gle.com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Sudeep Holla <sudeep.holla@....com>, Quentin Perret <qperret@...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 v7 0/2] Improve VM CPUfreq and task placement behavior

On Mon, Oct 28, 2024 at 4:39 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Sat, Oct 26, 2024 at 12:26 AM Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > On Tue, Oct 1, 2024 at 2:25 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > >
> > > On 18-09-24, 17:08, David Dai wrote:
> > > > Hi,
> > > >
> > > > This patch series is a continuation of the talk Saravana gave at LPC 2022
> > > > titled "CPUfreq/sched and VM guest workload problems" [1][2][3]. The gist
> > > > of the talk is that workloads running in a guest VM get terrible task
> > > > placement and CPUfreq behavior when compared to running the same workload
> > > > in the host. Effectively, no EAS(Energy Aware Scheduling) for threads
> > > > inside VMs. This would make power and performance terrible just by running
> > > > the workload in a VM even if we assume there is zero virtualization
> > > > overhead.
> > >
> > > > David Dai (2):
> > > >   dt-bindings: cpufreq: add virtual cpufreq device
> > > >   cpufreq: add virtual-cpufreq driver
> > > >
> > > >  .../cpufreq/qemu,virtual-cpufreq.yaml         |  48 +++
> > > >  drivers/cpufreq/Kconfig                       |  14 +
> > > >  drivers/cpufreq/Makefile                      |   1 +
> > > >  drivers/cpufreq/virtual-cpufreq.c             | 333 ++++++++++++++++++
> > > >  include/linux/arch_topology.h                 |   1 +
> > > >  5 files changed, 397 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/cpufreq/qemu,virtual-cpufreq.yaml
> > > >  create mode 100644 drivers/cpufreq/virtual-cpufreq.c
> > >
> > > LGTM.
> > >
> > > Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> >
> > Rafael/Viresh,
> >
> > Nudge... Any chance this will get pulled into 6.12?
>
> This is not a fix AFAICS, so 6.12 is out of the question.
>
> As for 6.13, Viresh thinks that this change is a good idea (or he
> wouldn't have ACKed it), so it's up to him.  I'm still not convinced
> that it will work on x86 or anything that doesn't use DT.

IIUC, we sent this patch before the 6.12 merge window closed. That's
why I was checking if we can get this into 6.12 :) And this is a new
driver, so the chances of this breaking anything in 6.12 is close to
zero.

> Viresh, I think that this falls into your bucket.

Anyway, 6.13 is fine, but would appreciate 6.12 (so we get it into LTS).

Thanks,
Saravana