Date: Mon, 23 Jun 2008 13:07:37 -0700
From: Arjan van de Ven <arjan@infradead.org>
To: Darren Hart <dvhltc@us.ibm.com>
Cc: paulmck@linux.vnet.ibm.com, 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: <20080623130737.489498dc@infradead.org>
In-Reply-To: <1214251374.4440.48.camel@Aeon>
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On Mon, 23 Jun 2008 20:02:54 +0000
Darren Hart <dvhltc@us.ibm.com> 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?
> 

so far, in practice, it's still single-digit amounts.

There's not that many timers that run normally. 
(based on powertop data from many systems)

-- 
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For development, discussion and tips for power savings, 
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