From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Galbraith Subject: Re: [Patch net] net_sched: replace yield() with cond_resched() Date: Wed, 05 Apr 2017 07:56:30 +0200 Message-ID: <1491371790.4536.151.camel@gmx.de> References: <1491357139-27108-1-git-send-email-xiyou.wangcong@gmail.com> <1491364545.4536.90.camel@gmx.de> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Linux Kernel Network Developers To: Cong Wang Return-path: Received: from mout.gmx.net ([212.227.15.19]:64326 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752346AbdDEF4d (ORCPT ); Wed, 5 Apr 2017 01:56:33 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2017-04-04 at 22:19 -0700, Cong Wang wrote: > On Tue, Apr 4, 2017 at 8:55 PM, Mike Galbraith 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... * 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