Re: CPU isolation question again

From: Luming Yu
Date: Wed Jul 04 2012 - 10:12:41 EST

On Wed, Jul 4, 2012 at 9:25 PM, Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:
> On Wed, Jul 04, 2012 at 08:42:29PM +0800, Luming Yu wrote:
>> On Tue, Jul 3, 2012 at 7:28 PM, Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:
>> > On Wed, Jun 27, 2012 at 09:22:09PM +0800, Luming Yu wrote:
>> >> Hi there,
>> >>
>> >> I noticed some discussion about CPU isolation which points me to the
>> >> patch set ( I'm currently
>> >> preparing a RFC-patch-set to automatically pick up a few suitable CPUs
>> >> to isolate then kick them out of service for a while. We need to
>> >> balance between thermal & power management And overall system
>> >> performance during this operation as much as possible. So
>> >> software-cpu-online-offline interface could not be a good option to
>> >> me. But to make sure I'm not blindly running on a dead-end path, I'd
>> >> check with experts here to ensure it makes some sense to isolate CPUs
>> >> to this level, and the idea also makes some sense, and the most
>> >> important is it's not implemented yet.
>> >
>> > I don't understand what you are trying to do and how exactly. How do you
>> > plan to do this isolation and how do you want to balance between thermal
>> > and power?
>> My question could be wrong as the question arose several weeks ago
>> when I came across
>> drivers/acpi/acpi_paid.c which looks like a real user who need to
>> request system automatically
>> pick up a few CPU to get them isolated and deactivated. Later on, I
>> noticed tglx's cpu hot plug re-work.
>> I realized we could reuse the interface to do isolation and deactivation work.
>> Of cause, to pick up which ones to isolate and deactivate is another problem.
>> cc'ed the author and ACPI maintainer of the driver as well as tglx.
> May be I'm confused because we both have our own definition of isolation.
> I'm not sure what kind of CPU isolation you're looking for.

At first, it needs not avaiable to scheduler. Then, it needs in
deepest power saving mode.
At last, it needs available to scheduler again on demand.
Sounds very like a typical soft offline cpu, but needs to be low light weight.
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