Date: Mon, 23 Jun 2008 13:15:16 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Darren Hart <dvhltc@us.ibm.com>
Cc: Arjan van de Ven <arjan@infradead.org>, linux-kernel@vger.kernel.org,
       mingo@elte.hu, josh@freedesktop.org, niv@us.ibm.com, dino@in.ibm.com,
       akpm@linux-foundation.org, torvalds@linux-foundation.org,
       vegard.nossum@gmail.com, adobriyan@gmail.com, oleg@tv-sign.ru,
       bunk@kernel.org, rjw@sisk.pl
Subject: Re: [PATCH -tip-rcu] Make rcutorture more vicious: make quiescent rcutorture less power-hungry
Message-ID: <20080623201516.GC10595@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <20080618122144.GA27143@linux.vnet.ibm.com> <20080618162649.GA18326@linux.vnet.ibm.com> <20080622200638.GA25328@linux.vnet.ibm.com> <20080622131712.54ba732c@infradead.org> <1214243649.4440.10.camel@Aeon> <20080623110706.197f25b1@infradead.org> <1214251374.4440.48.camel@Aeon>
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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@us.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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