Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932562AbbELM0F (ORCPT ); Tue, 12 May 2015 08:26:05 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:60424 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932314AbbELM0C (ORCPT ); Tue, 12 May 2015 08:26:02 -0400 Date: Tue, 12 May 2015 14:25:45 +0200 From: Peter Zijlstra To: Julian Anastasov Cc: Ingo Molnar , Linus Torvalds , Oleg Nesterov , linux-kernel@vger.kernel.org, neilb@suse.de Subject: Re: [PATCH] sched: Introduce TASK_NOLOAD and TASK_IDLE Message-ID: <20150512122545.GN21418@twins.programming.kicks-ass.net> References: <20150508124748.GH27504@twins.programming.kicks-ass.net> <20150511142247.GT27504@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2185 Lines: 54 On Mon, May 11, 2015 at 10:34:11PM +0300, Julian Anastasov wrote: > On Mon, 11 May 2015, Peter Zijlstra wrote: > > > > - schedule_timeout_idle (instead of schedule_timeout call): > > > __set_current_state(TASK_IDLE); > > > return schedule_timeout(timeout); > > > > > > - we here are really idle, so "N" looks ok > > > > So I don't get the point of the schedule_timeout_*() stubs. What are > > they for? Why would one use an unconditional schedule_timeout() call? > > Isn't that what msleep() is for? > > msleep will not return until timeout has expired. > Instead, we want to notice the kthread_should_stop() event > immediately. Additionally, TASK_UNINTERRUPTIBLE will increase > the load average. We can do it with extra wait queue > and the new __wait_event_idle_timeout but I guess > schedule_timeout_idle will be a good replacement for > schedule_timeout_interruptible calls when used for kthreads. Fair enough I suppose, but then calling it schedule*() is just plain wrong, it does not behave/act like a normal schedule() call. Lemme go look at how widely abused that is. *sigh*, its all over the place :/ $ git grep "schedule_timeout_\(interruptible\|killable\|uninterruptible\)" | wc -l 392 That said; I still don't see the point of schedule_timeout_idle(), we should not sleep poll for state like that. We should only use TASK_IDLE when we are in fact _IDLE_ and do not have work to do, at which point one should use an wait_event() like construct to wait for new work. > > + * like wait_event_timeout() -- except it uses TASK_IDLE to avoid loadavg > > + */ > > +#define wait_event_idle_timeout(wq, condition, timeout) \ > > +({ \ > > + long __ret = timeout; \ > > + might_sleep(); \ > > + if (!___wait_cond_timeout(condition)) \ > > + ret = __wait_event_idle_timeout(wq, condition, timeout);\ > > ret may need underscores here... I'm fairly sure that might aid in compilation indeed :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/