linux-kernel - Re: [PATCH -tip-rcu] Make rcutorture more vicious: make quiescent rcutorture less power-hungry

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Message-ID: <20080623201516.GC10595@linux.vnet.ibm.com>
Date:	Mon, 23 Jun 2008 13:15:16 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, josh@...edesktop.org,
	niv@...ibm.com, dino@...ibm.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, vegard.nossum@...il.com,
	adobriyan@...il.com, oleg@...sign.ru, bunk@...nel.org, rjw@...k.pl
Subject: Re: [PATCH -tip-rcu] Make rcutorture more vicious: make quiescent rcutorture less power-hungry

On Mon, Jun 23, 2008 at 08:02:54PM +0000, Darren Hart wrote:
> On Mon, 2008-06-23 at 11:07 -0700, Arjan van de Ven wrote:
> > On Mon, 23 Jun 2008 17:54:09 +0000
> > Darren Hart <dvhltc@...ibm.com> wrote:
> > 
> > > I'm a little concerned about how this will affect real-time
> > > performance, as queueing up lots of timers all at once can lead to
> > > long running timer expiration handlers.  If just a schedule_timeout,
> > > I suppose we are only looking at a process wakeup, as opposed to a
> > > softirq context callback function?
> > 
> > in reality, the time it takes to deliver the interrupt (including
> > waking the CPU up etc), is likely to be an order or two of magnitude
> > higher than this kind of code loop.... 
> 
> Sure, if we just look at one of them.  Any idea how many such items
> we're looking at rounding up to fire at the same time?  Is it dozens,
> hundreds, thousands?

Hello, Darren,

Wouldn't these timers be running at low priority, so that high-priority
realtime tasks would preempt them?

							Thanx, Paul
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