From: Mike Galbraith <efault@gmx•de>
To: Cong Wang <xiyou.wangcong@gmail•com>
Cc: Linux Kernel Network Developers <netdev@vger•kernel.org>
Subject: Re: [Patch net] net_sched: replace yield() with cond_resched()
Date: Wed, 05 Apr 2017 07:56:30 +0200 [thread overview]
Message-ID: <1491371790.4536.151.camel@gmx.de> (raw)
In-Reply-To: <CAM_iQpXpZjpS1ZG7hH-52jt41FzzyMZ0rss9PauaSD54XSQiXQ@mail.gmail.com>
On Tue, 2017-04-04 at 22:19 -0700, Cong Wang wrote:
> On Tue, Apr 4, 2017 at 8:55 PM, Mike Galbraith <efault@gmx•de> wrote:
> > That won't help, cond_resched() has the same impact upon a lone
> > SCHED_FIFO task as yield() does.. none.
>
> Hmm? In the comment you quote:
>
> * If you want to use yield() to wait for something, use wait_event().
> * If you want to use yield() to be 'nice' for others, use cond_resched().
>
> So if cond_resched() doesn't help, why this misleading comment?
This is not an oh let's be nice guys thing, it's a perfect match of...
<copy/paste>
* while (!event)
* yield();
(/copy/paste>
..get off the CPU until this happens thing. With nobody to yield the C
PU to, some_qdisc_is_busy() will remain true forever more.
> I picked the latter one, because the former is harder to implement
> properly (at least for -net) we need qdisc's to notify this waiter once
> they finish transmitting packets, which means we probably need
> a per-netdevice wait struct.
Yup, why I merely notified net-fu masters of lurking spinner. I met it
because I sometimes run most kthreads at prio 1, some prioritized, and
kworkers at prio 2. (never mind why, but they're excellent reasons)
-Mike
next prev parent reply other threads:[~2017-04-05 5:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-05 1:52 [Patch net] net_sched: replace yield() with cond_resched() Cong Wang
2017-04-05 3:55 ` Mike Galbraith
2017-04-05 5:19 ` Cong Wang
2017-04-05 5:56 ` Mike Galbraith [this message]
2017-04-05 23:42 ` Cong Wang
2017-04-06 1:54 ` Mike Galbraith
2017-04-06 22:13 ` Stephen Hemminger
2017-04-07 3:59 ` Mike Galbraith
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