linux-kernel - Re: [git pull request] ACPI Processor Aggregator Driver for 2.6.32-rc1

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Date:	Tue, 6 Oct 2009 02:03:37 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Len Brown <lenb@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-acpi@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Shaohua Li <shaohua.li@...el.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: [git pull request] ACPI Processor Aggregator Driver for
 2.6.32-rc1

* Rafael J. Wysocki <rjw@...k.pl> [2009-10-05 21:59:24]:

> On Monday 05 October 2009, Balbir Singh wrote:
> > * Len Brown <lenb@...nel.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@...el.com>
> > >     NACKed-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > >     Cc: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
> > >     Signed-off-by: Len Brown <len.brown@...el.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@...el.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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