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

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Date:	Mon, 23 Jun 2008 13:07:37 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	paulmck@...ux.vnet.ibm.com, 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, 23 Jun 2008 20:02:54 +0000
Darren Hart <dvhltc@...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@...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)

-- 
If you want to reach me at my work email, use arjan@...ux.intel.com
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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