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SubjectRe: [git pull request] ACPI Processor Aggregator Driver for 2.6.32-rc1
* Rafael J. Wysocki <rjw@sisk.pl> [2009-10-05 21:59:24]:

> On Monday 05 October 2009, Balbir Singh wrote:
> > * Len Brown <lenb@kernel.org> [2009-10-03 01:56:32]:
> >
> > > This driver does not use the kernel's CPU hot-plug mechanism
> > > because after the transient emergency is over, the system must
> > > be returned to its normal state, and hotplug would permanently
> > > break both cpusets and binding.
> > >
> >
> > Why does hotplug break cpusets and binding?
> >
> >
> > > So to force idle, the driver creates a power saving thread.
> > > The scheduler will migrate the thread to the preferred CPU.
> > > The thread has max priority and has SCHED_RR policy,
> > > so it can occupy one CPU. To save power, the thread will
> > > invoke the deep C-state entry instructions.
> > >
> > > To avoid starvation, the thread will sleep 5% of the time
> > > time for every second (current RT scheduler has threshold
> > > to avoid starvation, but if other CPUs are idle,
> > > the CPU can borrow CPU timer from other,
> > > which makes the mechanism not work here)
> > >
> > > Vaidyanathan Srinivasan has proposed scheduler enhancements
> > > to allow injecting idle time into the system. This driver doesn't
> > > depend on those enhancements, but could cut over to them
> > > when they are available.
> > >
> > > Peter Z. does not favor upstreaming this driver until
> > > the those scheduler enhancements are in place. However,
> > > we favor upstreaming this driver now because it is useful
> > > now, and can be enhanced over time.
> > >
> > > Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> > > NACKed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > > Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
> > > Signed-off-by: Len Brown <len.brown@intel.com>
> >
> > This is a first a patch with a NACKed-by, could we please have more
> > discussion on the proposed design.
>
> This thing has already been merged, it appears:
>

Yeah.. just saw it in my kernel compile today!

> commit 8e0af5141ab950b78b3ebbfaded5439dcf8b3a8d
> Author: Shaohua Li <shaohua.li@intel.com>
> Date: Mon Jul 27 18:11:02 2009 -0400
>
> ACPI: create Processor Aggregator Device driver
>
> and it looks like a total breakage of rules to me.
>
> Thanks,
> Rafael

--
Balbir


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