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

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Message-ID: <Zx-I_PhsEhnEUfSf@bogus>
Date: Mon, 28 Oct 2024 12:52:12 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Saravana Kannan <saravanak@...gle.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	David Dai <davidai@...gle.com>, Rob Herring <robh@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	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 01:43:38PM +0100, Rafael J. Wysocki wrote:
> On Mon, Oct 28, 2024 at 1:33 PM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Mon, Oct 28, 2024 at 12:39:31PM +0100, Rafael J. Wysocki 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.
> > >
> >
> > +1, I was about to comment on DT bindings patch, but then I assumed it is
> > accepted to have a device object with similar CID and CRS(for register address)
> > in ACPI for example.
> 
> Well, where would the device ID be defined for this?  The spec or
> somewhere else?  If the latter, then where again?
>

Yes, we need to figure those details, but I assumed that is the general
idea to get it working in ACPI. We can figure out details when we have to
add it.

> > But yes, the patch itself is not adding support for that
> > yet. If not is not the way, then we need to come up with a way that works
> > for both ACPI and DT.
> 
> The DT use case is there I think and so I don't want to block it just
> because there is no ACPI counterpart.  It can be added later if the
> use case is relevant enough.

Agreed and that was my thoughts as well.

--
Regards,
Sudeep