linux-kernel - Re: [PATCH] ksoftirqd: Enable IRQs and call cond

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Date:	Wed, 21 Jan 2015 07:29:39 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Calvin Owens <calvinowens@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joe Perches <joe@...ches.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH] ksoftirqd: Enable IRQs and call cond_resched() before
 poking RCU

On Tue, 2015-01-20 at 21:10 -0800, Paul E. McKenney wrote: 
> On Wed, Jan 21, 2015 at 04:40:39AM +0100, Mike Galbraith wrote:

> > I've been curious about this for ages, so now is a great time to bite
> > the bullet and ask TheMan.  A context switch is not far away, why do we
> > need that quiescent state badly enough to tell what looks like a little
> > white lie to get it immediately?
> > 
> > (I commented it out in an -rt kernel I was testing yesterday, beat it
> > enthusiastically for a while, and box didn't _seem_ to notice that it
> > was missing anything)
> 
> Yeah, you do have to have a fairly violent network-based DoS attack
> to see the difference.  Robert Olsson was the first to make this happen
> back in the day.

Ah, my little NIC doesn't have enough poop to do that.  Thanks.

-Mike

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