Re: [PATCH 0/6] RFC: CPU frequency min/max as PM QoS params

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Monday, January 09, 2012, mark gross wrote:
> On Sun, Jan 08, 2012 at 11:59:24PM +0100, Rafael J. Wysocki wrote:
> > On Friday, January 06, 2012, mark gross wrote:
> > > On Fri, Jan 06, 2012 at 02:36:20AM +0200, Antti P Miettinen wrote:
> > > > The inspiration for this patch series is the N9 CPU frequency boost
> > > > upon input events:
> > > > 
> > > > http://www.spinics.net/lists/cpufreq/msg00667.html
> > > > 
> > > > and the related changes in git://codeaurora.org/kernel/msm.git tree.
> > > > Those patches modify the ondemand cpufreq governor. This patch series
> > > > adds minimum and maximum CPU frequency as PM QoS parameters and
> > > > modifies the cpufreq core to enforce the PM QoS limits. There is also
> > > > an example module for boosting the frequency upon input events.
> > > > 
> > > > I've been testing these changes against Ubuntu 3.2 kernel on a Dell
> > > > E6420 with the ACPI cpufreq driver. The patches are against
> > > > linux-next/master, compile tested against it.
> > > > 
> > > > 	--Antti
> > > > 
> > > > Alex Frid (1):
> > > >   PM QoS: Simplify PM QoS expansion/merge
> > > > 
> > > > Antti P Miettinen (5):
> > > >   PM QoS: Add CPU frequency min/max as PM QoS params
> > > >   cpufreq: Export user_policy min/max
> > > >   cpufreq: Preserve sysfs min/max request
> > > >   cpufreq: Enforce PM QoS min/max limits
> > > >   input: CPU frequency booster
> > > > 
> > > >  drivers/cpufreq/cpufreq.c     |   57 +++++++++++++-
> > > >  drivers/input/Kconfig         |    9 ++
> > > >  drivers/input/Makefile        |    1 +
> > > >  drivers/input/input-cfboost.c |  174 +++++++++++++++++++++++++++++++++++++++++
> > > >  include/linux/pm_qos.h        |   19 ++++-
> > > >  kernel/power/qos.c            |   55 ++++++++++----
> > > >  6 files changed, 293 insertions(+), 22 deletions(-)
> > > >  create mode 100644 drivers/input/input-cfboost.c
> > > > 
> > > 
> > > The following is my version of part of this patch set I was tinkering
> > > with.  Its missing the cpufreq notification this change has and doesn't
> > > do anything WRT cfboost.
> > > 
> > > Would it be ok if we could consolidate our two implementations and
> > > completely separate the cfboost stuff as a separate patch set?
> > > 
> > > My code below is missing the cpufreq notification logic you have.
> > 
> > Well, I have one substantial problem with this approach.  Namely, our
> > current PM QoS infrastructure is not suitable for throughput constraints,
> > because they should be additive, unlike the latency ones.
> > 
> > Namely, if sombody requests throughput X and someone else Y, the resulting
> > combined throughput should be X+Y rather than max(X, Y).
> 
> That can be done easy enough.  However; in practice I'm not convinced
> doing and additive aggregation of the requested QoS would be any better
> than just taking the max.

Well, I'd say it's necessary for correctness, perhaps not for the CPU, but in
general.  If Y is the max, then the subsystem that requested X may easily
starve whoever requested the Y by using all of the bandwidth it asked for.

> But, we can give it a try.

Good. :-)

Thanks,
Rafael