From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161104AbXCAWwi (ORCPT ); Thu, 1 Mar 2007 17:52:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161116AbXCAWwh (ORCPT ); Thu, 1 Mar 2007 17:52:37 -0500 Received: from proxima.lp0.eu ([85.158.45.36]:42168 "EHLO proxima.lp0.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161102AbXCAWwJ (ORCPT ); Thu, 1 Mar 2007 17:52:09 -0500 Message-ID: <45E75911.3070907@simon.arlott.org.uk> Date: Thu, 01 Mar 2007 22:52:01 +0000 From: Simon Arlott User-Agent: Thunderbird 1.5.0.5 (X11/20060819) MIME-Version: 1.0 To: Linux Kernel Mailing List CC: akpm@linux-foundation.org, arjan@linux.intel.com Subject: Re: [PATCH (updated)] timer: Run calc_load halfway through each round_jiffies second References: <45E0577C.9020409@simon.arlott.org.uk> <45E698DF.4010006@simon.arlott.org.uk> <45E720E8.1010809@simon.arlott.org.uk> In-Reply-To: <45E720E8.1010809@simon.arlott.org.uk> X-Enigmail-Version: 0.94.1.2 OpenPGP: id=89C93563 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Whenever jiffies is started at a multiple of 5*HZ or wraps, calc_load is run exactly on the second which is when tasks using round_jiffies will be scheduled to run. This has a bad effect on the load average, making it tend towards 1.00 if a task happens to run every time the load is being calculated. This changes calc_load so that it updates load half a second after any tasks scheduled using round_jiffies. Signed-off-by: Simon Arlott Cc: Andrew Morton Cc: Arjan van de Ven --- Without this change or an appropriate equivalent, my change to cxacru causes the load to stay around 1.00 even when mostly idle since it now runs every second using round_jiffies: > [ 332.416288] cxacru_poll_status(..), jiffies=5000 [start] > [ 332.417312] calc_load(1), count=-1, jiffies=5001 [start] > [ 332.417322] calc_load(1), count=4999, jiffies=5001 [finish] > [ 332.423382] cxacru_poll_status(..), jiffies=5007, next=993 [finish] kernel/timer.c | 8 +++++--- 1 files changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/timer.c b/kernel/timer.c index cb1b86a..ee61f6c 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -1225,17 +1225,19 @@ EXPORT_SYMBOL(avenrun); static inline void calc_load(unsigned long ticks) { unsigned long active_tasks; /* fixed-point */ - static int count = LOAD_FREQ; + static int count = LOAD_FREQ + HZ/2; count -= ticks; - if (unlikely(count < 0)) { + if (unlikely(count <= 0)) { active_tasks = count_active_tasks(); do { CALC_LOAD(avenrun[0], EXP_1, active_tasks); CALC_LOAD(avenrun[1], EXP_5, active_tasks); CALC_LOAD(avenrun[2], EXP_15, active_tasks); count += LOAD_FREQ; - } while (count < 0); + } while (count <= 0); + + count = round_jiffies_relative(count + HZ/2) - HZ/2; } } -- 1.5.0.1 -- Simon Arlott