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

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Message-ID: <1394166397.5056.40.camel@marge.simpson.net>
Date:	Fri, 07 Mar 2014 05:26:37 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	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 calls

On Thu, 2014-03-06 at 16:06 -0500, David Miller wrote: 
> From: Marc Kleine-Budde <mkl@...gutronix.de>
> Date: Wed,  5 Mar 2014 00:49:47 +0100
> 
> > @@ -839,7 +839,7 @@ void dev_deactivate_many(struct list_head *head)
> >  	/* Wait for outstanding qdisc_run calls. */
> >  	list_for_each_entry(dev, head, unreg_list)
> >  		while (some_qdisc_is_busy(dev))
> > -			yield();
> > +			msleep(1)
> >  }
> 
> I don't understand this.
> 
> yield() should really _mean_ yield.

It does, but yield() semantics make it useless for what you want to do..
and pretty much undefined for anything other than SCHED_FIFO.  If you
really want to give up the CPU to any old body, you have to sleep.

-Mike




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