Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1768977Ab2KOUgD (ORCPT ); Thu, 15 Nov 2012 15:36:03 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:29759 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1768934Ab2KOUgA (ORCPT ); Thu, 15 Nov 2012 15:36:00 -0500 X-Authority-Analysis: v=2.0 cv=dvhZ+ic4 c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=JomeGkWH5N8A:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=meVymXHHAAAA:8 a=kXjThILi--AA:10 a=pGLkceISAAAA:8 a=VwQbUJbxAAAA:8 a=W0vUJOdyAAAA:8 a=bDuOARI7VrL81TyMe3cA:9 a=PUjeQqilurYA:10 a=x8gzFH9gYPwA:10 a=MSl-tDqOz04A:10 a=47_JZSdGUwyKkP8f:21 a=2pO86J1KDKP4M0YI:21 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.115.198 Message-ID: <1353011758.18025.123.camel@gandalf.local.home> Subject: Re: [sched/rt] Optimization of function pull_rt_task() From: Steven Rostedt To: Yong Zhang Cc: Kirill Tkhai , "linux-kernel@vger.kernel.org" , Ingo Molnar , Peter Zijlstra Date: Thu, 15 Nov 2012 15:35:58 -0500 In-Reply-To: <20120604052755.GA28710@zhy> References: <1334519122.8698.3.camel@hp> <1334592379.28106.4.camel@gandalf.stny.rr.com> <1334773976.28106.49.camel@gandalf.stny.rr.com> <1334783815.28106.56.camel@gandalf.stny.rr.com> <20120419085440.GC3963@zhy> <69791338569116@web3f.yandex.ru> <20120604052755.GA28710@zhy> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.4.3-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6335 Lines: 181 Doing my INBOX maintenance (clean up), I've stumbled on this thread again. I'm not sure the changes here are hopeless. On Mon, 2012-06-04 at 13:27 +0800, Yong Zhang wrote: > On Fri, Jun 01, 2012 at 08:45:16PM +0400, Kirill Tkhai wrote: > > > > > > 19.04.2012, 12:54, "Yong Zhang" : > > > On Wed, Apr 18, 2012 at 05:16:55PM -0400, Steven Rostedt wrote: > > > > > >> ?On Wed, 2012-04-18 at 14:32 -0400, Steven Rostedt wrote: > > >>> ?On Mon, 2012-04-16 at 12:06 -0400, Steven Rostedt wrote: > > >>>> ?On Sun, 2012-04-15 at 23:45 +0400, Kirill Tkhai wrote: > > >>>>> ?The condition (src_rq->rt.rt_nr_running) is weak because it doesn't > > >>>>> ?consider the cases when src_rq has only processes bound to it (when > > >>>>> ?single cpu is allowed). It may be running kernel thread like > > >>>>> ?migration/x etc. > > >>>>> > > >>>>> ?So it's better to use more stronger condition which is able to exclude > > >>>>> ?above conditions. The function has_pushable_tasks() complitely does > > >>>>> ?this. A task may be pullable for another cpu rq only if he is pushable > > >>>>> ?for his own queue. > > >>>> ?I considered this before, and for some reason I never did the change. > > >>>> ?I'll have to think about it. It seems like this would be the obvious > > >>>> ?case, but I think there was something not so obvious that caused issues. > > >>>> ?But I don't remember what it was. > > >>>> > > >>>> ?I'll have to rethink this again. > > >>> ?I can't find anything wrong with this change. Maybe things change, or I > > >>> ?was thinking of another change. > > >>> > > >>> ?I'll apply it and start running my tests against it. > > >> ?Not only does this seem to work fine, I took it one step further :-) > > > > > > Hmm... throttle doesn't handle the pushable list, so we may find a > > > throttled task by pick_next_pushable_task(). > > > > > > Thanks, > > > Yong > > > > I don't complitelly understand throttle logic. > > > > Is the source patch not-appliable the same reason? > > I guess so. > > Your patch will change the semantic of pick_next_pushable_task(). Looking at the original patch, I don't see how it changes the semantics (although mine may have). The original patch was: --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1729,7 +1729,7 @@ static int pull_rt_task(struct rq *this_rq) /* * Are there still pullable RT tasks? */ - if (src_rq->rt.rt_nr_running <= 1) + if (!has_pushable_tasks(src_rq)) goto skip; p = pick_next_highest_task_rt(src_rq, this_cpu); And I still don't see a problem with this. If a rq has no pushable tasks, then we shouldn't bother trying to pull from it (no task can migrate). Thus, the original patch, I believe should be applied without question. Now, about my patch, the one that made pick_next_highest_task_rt into just: static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu) { struct plist_head *head = &rq->rt.pushable_tasks; struct task_struct *next; plist_for_each_entry(next, head, pushable_tasks) { if (pick_rt_task(rq, next, cpu)) return next; } return NULL; } You said could pick a task from a throttled rq. I'm not sure that is different than what we have now. As the current pick_next_highest_task_rt() just does a loop over the leaf_rt_rqs which includes throttled rqs. That's because a throttled rq will not dequeue the rt_rq from the leaf_rt_rq list if the rt_rq has rt_nr_running != 0. I'm still thinking about adding both patches. -- Steve > > Thanks, > Yong > > > > > Kirill > > > > > > > >> ?Peter, do you see anything wrong with this patch? > > >> > > >> ?-- Steve > > >> > > >> ?diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > > >> ?index 61e3086..b44fd1b 100644 > > >> ?--- a/kernel/sched/rt.c > > >> ?+++ b/kernel/sched/rt.c > > >> ?@@ -1416,39 +1416,15 @@ static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu) > > >> ??/* Return the second highest RT task, NULL otherwise */ > > >> ??static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu) > > >> ??{ > > >> ?- struct task_struct *next = NULL; > > >> ?- struct sched_rt_entity *rt_se; > > >> ?- struct rt_prio_array *array; > > >> ?- struct rt_rq *rt_rq; > > >> ?- int idx; > > >> ?+ struct plist_head *head = &rq->rt.pushable_tasks; > > >> ?+ struct task_struct *next; > > >> > > >> ?- for_each_leaf_rt_rq(rt_rq, rq) { > > >> ?- array = &rt_rq->active; > > >> ?- idx = sched_find_first_bit(array->bitmap); > > >> ?-next_idx: > > >> ?- if (idx >= MAX_RT_PRIO) > > >> ?- continue; > > >> ?- if (next && next->prio <= idx) > > >> ?- continue; > > >> ?- list_for_each_entry(rt_se, array->queue + idx, run_list) { > > >> ?- struct task_struct *p; > > >> ?- > > >> ?- if (!rt_entity_is_task(rt_se)) > > >> ?- continue; > > >> ?- > > >> ?- p = rt_task_of(rt_se); > > >> ?- if (pick_rt_task(rq, p, cpu)) { > > >> ?- next = p; > > >> ?- break; > > >> ?- } > > >> ?- } > > >> ?- if (!next) { > > >> ?- idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1); > > >> ?- goto next_idx; > > >> ?- } > > >> ?+ plist_for_each_entry(next, head, pushable_tasks) { > > >> ?+ if (pick_rt_task(rq, next, cpu)) > > >> ?+ return next; > > >> ??????????} > > >> > > >> ?- return next; > > >> ?+ return NULL; > > >> ??} > > >> > > >> ??static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask); > > >> > > >> ?-- > > >> ?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/ > > > -- > > > Only stand for myself > > -- > > 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/ > -- 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/