linux-kernel - Re: [NET]: rt_check_expire() can take a long time, add a cond

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Message-Id: <20071115.200714.109055797.davem@davemloft.net>
Date:	Thu, 15 Nov 2007 20:07:14 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	arjan@...radead.org
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	dada1@...mosbay.com
Subject: Re: [NET]: rt_check_expire() can take a long time, add a
 cond_resched()

From: Arjan van de Ven <arjan@...radead.org>
Date: Thu, 15 Nov 2007 19:38:02 -0800

> On Thu, 15 Nov 2007 04:01:48 GMT
> Linux Kernel Mailing List <linux-kernel@...r.kernel.org> wrote:
> 
> >     Using a "if (need_resched())" test before calling
> > "cond_resched();" is necessary to avoid spending too much time doing
> > the resched check. 
> 
> int __sched cond_resched(void)
> {
>         if (need_resched() &&  .....
> 
> somehow I wonder why the second if() is useful at all; it's another
> spot for a branch predictor to miss... and a void function call is
> really really cheap... 

Not by Eric's tests.  Please read the thread, he checked and it's
50ms more expensive to make the function call.

Please, when you notice something interesting in something flying
by on git-web, go check thing out we probably discussed the thing
you're interested in.

And please at least CC: netdev about networking patches, and also the
patch author, which I've corrected in this reply.
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