Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756044Ab3HFNXs (ORCPT ); Tue, 6 Aug 2013 09:23:48 -0400 Received: from mail-lb0-f181.google.com ([209.85.217.181]:45248 "EHLO mail-lb0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755872Ab3HFNXr (ORCPT ); Tue, 6 Aug 2013 09:23:47 -0400 MIME-Version: 1.0 Date: Tue, 6 Aug 2013 21:23:46 +0800 Message-ID: Subject: false nr_running check in load balance? From: Lei Wen To: Paul Turner , linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , leiwen@marvell.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1869 Lines: 48 Hi Paul, I notice in load_balance function, it would check busiest->nr_running to decide whether to perform the real task movement. But in some case, I saw the nr_running is not matching with the task in the queue, which seems make scheduler to do many redundant checking. What I means is like there is only one task in the queue, but nr_running shows it has two. So if that task cannot be moved, it would be still checked for twice. With further checking, I find there is one patch you submit before: commit 953bfcd10e6f3697233e8e5128c611d275da39c1 Author: Paul Turner Date: Thu Jul 21 09:43:27 2011 -0700 sched: Implement hierarchical task accounting for SCHED_OTHER In this patch, you increase nr_running when enqueue enqueue_task_stop, which is the reason nr_running is increase while task not be increased. It is true at that time, the stopper has been waken up and enqueue again into cpu, and do the migration job. So the logic should be right there. My question is whether we could change the judgment into cfs_rq->nr_running? Since the load_balance is only for cfs, right? diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bb456f4..ffc0d35 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5096,7 +5096,7 @@ redo: schedstat_add(sd, lb_imbalance[idle], env.imbalance); ld_moved = 0; - if (busiest->nr_running > 1) { + if (busiest->cfs.nr_running > 1) { /* * Attempt to move tasks. If find_busiest_group has found * an imbalance but busiest->nr_running <= 1, the group is Thanks, Lei -- 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/