linux-kernel - Re: [RFC PATCH v2 0/5] sched: modular find_busiest

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Date:	Fri, 24 Oct 2008 15:34:58 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	David Collier-Brown <davecb@....com>,
	Tim Connors <tconnors@...ro.swin.edu.au>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Gregory Haskins <ghaskins@...ell.com>,
	arjan <arjan@...radead.org>
Subject: Re: [RFC PATCH v2 0/5] sched: modular find_busiest_group()

* Peter Zijlstra <peterz@...radead.org> [2008-10-14 15:25:03]:

> On Tue, 2008-10-14 at 18:37 +0530, Vaidyanathan Srinivasan wrote:
> > * Peter Zijlstra <peterz@...radead.org> [2008-10-14 14:09:13]:
> > 
> > > 
> > > Hi,
> > > 
> > > So the basic issue is sched_group::cpu_power should become more dynamic.
> > 
> > Hi Peter,
> > 
> > This is a good idea.  Dynamically increasing cpu power to some groups
> > will automatically help power savings when we want to consolidate
> > better to one cpu package when overall system utilisation is very low.  
> 
> Ah, yes another use case of this ;-)
> 
> > > Dynamic Speed Technology
> > > ------------------------
> > > 
> > > With cpus actively fiddling with their processing capacity we get into
> > > similar issues. Again we can measure this, but this would require the
> > > addition of a clock that measures work instead of time.
> > > 
> > > Having that, we can even acturately measure the old SMT case, which has
> > > always been approximated by a static percentage - even though the actual
> > > gain is very workload dependent.
> > > 
> > > The idea is to introduce sched_work_clock() so that:
> > > 
> > >         work_delta / time_delta gives the power for a cpu. <1 means we
> > >         did less work than a dedicated pipeline, >1 means we did more.
> > 
> > The challenge here is measurement of 'work'.  What will be the
> > parameter that will be fair for most workloads and easy to measure on
> > most systems?
> > 
> > * Instructions completion count
> > * APERF or similar CPU specific counter on x86
> > * POWER has PURR and SPURR to have a measure of relative work done  
> 
> Right - I was hoping for some feedback from the arch folks (maybe I
> should have CC'ed linux-arch) on this issue.

Hi Peter,

Do you want to post this RFD again to get more feedback? 

--Vaidy
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