linux-kernel - Re: [RFC PATCH v5 4/7] sched: bias task wakeups to preferred semi-idle packages

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Message-ID: <20081216072502.GW5457@dirshya.in.ibm.com>
Date:	Tue, 16 Dec 2008 12:55:02 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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>,
	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>,
	Gregory Haskins <gregory.haskins@...il.com>
Subject: Re: [RFC PATCH v5 4/7] sched: bias task wakeups to preferred
	semi-idle packages

* Balbir Singh <balbir@...ux.vnet.ibm.com> [2008-12-15 23:32:36]:

> >> > > Sure its racy, but so what?
> >> > >
> >> > > The worst I can see it that we exclude a dying task from this logic,
> >> > > which isn't a problem at all, since its dying anyway.
> >> >
> >> > At which point I seriously doubt it'd still be on the rq anyway.
> >> >
> >>
> >> I forgot to mention that, the check should be (p->mm && !(p->flags & PF_KTHREAD))
> >
> > I can check for PF_KTHREAD for now.  However, I should reduce the
> > number of checks since this may slow down wake_idle for sched_mc=2.
> >
> > We can tolerate p->mm check on a dying process as Peter has suggested,
> > hence we don't need to protect it.  We are not going to access any
> > contents of the mm struct.
> >
> > If PF_KTHREAD is only being used by AIO, then I feel we can drop the
> > check since the threads will not have affinity and they can be moved
> > to other cpus anyway.
> >
> > The main reason for skipping kthread is that they may be using per-cpu
> > variables and sleep/preempted.  I did not want the wake_idle() logic
> > to move them around forcefully.  This is not the general case and this
> > situation should not happen.
> >
> > Second reason is to optimise on the affinity check since most of the
> > kthreads have affinity and cannot be moved.
> >
> > This condition check needs optimisation after getting the framework
> > functionally correct and useful.
> 
> 
> Vaidy, you (or your mailer) seem to have dropped me off of the to/cc
> list while replying and this seems to be the case for all replies.

Hi Balbir,

Thanks for pointing that out.  I will review my mutt setup.  This is
strange... since a group-reply to this message puts you in the to list
as expected, but not the ones that I sent earlier in reply to your
messages.  The header seems to be correct for others except for your
message :(

--Vaidy
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