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

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Message-ID: <661de9470812151002h15e523b0s85bf1537d6e7f5fe@mail.gmail.com>
Date:	Mon, 15 Dec 2008 23:32:36 +0530
From:	"Balbir Singh" <balbir@...ux.vnet.ibm.com>
To:	svaidy@...ux.vnet.ibm.com, "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

>> > > 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.

Balbir
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