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SubjectRe: [PATCH] net: sched: dev_deactivate_many(): use msleep(1) instead of yield() to wait for outstanding qdisc_run calls
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On Thu, 2014-03-06 at 16:06 -0500, David Miller wrote:
> From: Marc Kleine-Budde <mkl@pengutronix.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.
>
> The intent of a yield() call, like this one here, is unambiguously
> that the current thread cannot do anything until some other thread
> gets onto the cpu and makes forward progress.
>
> Therefore it should allow lower priority threads to run, not just
> equal or higher priority ones.

Until when?

yield() is not a sensible operation in a preemptive multitasking system,
regardless of RT.

Ben.

--
Ben Hutchings
I say we take off; nuke the site from orbit. It's the only way to be sure.
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