netdev - Re: [PATCH] net: sched: dev_deactivate_many(): use msleep(1) instead of yield() to wait for outstanding qdisc

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Message-ID: <20140407111906.GH11096@twins.programming.kicks-ass.net>
Date:	Mon, 7 Apr 2014 13:19:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, tglx@...utronix.de, ben@...adent.org.uk,
	mkl@...gutronix.de, linux-rt-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	kernel@...gutronix.de
Subject: Re: [PATCH] net: sched: dev_deactivate_many(): use msleep(1) instead
 of yield() to wait for outstanding qdisc_run callsb

On Fri, Apr 04, 2014 at 11:26:28AM -0400, David Miller wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Fri, 4 Apr 2014 17:19:42 +0200
> 
> > The proper way to fix the dev_deactivate_many() is to use wait_event(),
> > polling for that state is just daft. Afaict there is no reason the qdisc
> > code could not do a wakeup whenever that condition changes.
> 
> I actually looked into this, and it's going to add expensive checks
> to the fast paths of packet processing.
> 
> If it was so easy we'd be doing it that way already.

Fair enough; and I suppose this waiting side is 'rare' compared to the
packet processing side of things?

In that case you could add a comment with the msleep() and just leave it
at that I suppose.
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