linux-kernel - round_jiffies and load average

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Date:	Sat, 24 Feb 2007 15:19:24 +0000
From:	Simon Arlott <simon@...ott.org>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: round_jiffies and load average

I've modified the driver of an USB device (cxacru) to schedule the next poll for status every 1s using round_jiffies_relative instead of just waiting 1s since the last poll was completed. This process takes on average 11ms to complete and while it is waiting for a response it's considered running.

The load average is calculated every 5 seconds equivalent to round_jiffies, so I have a problem with the load average always tending towards 1.00:

 14:26:19 up 6 days, 14:45,  5 users,  load average: 1.10, 1.04, 1.02
 14:27:19 up 6 days, 14:46,  5 users,  load average: 1.03, 1.03, 1.01
 14:28:19 up 6 days, 14:47,  5 users,  load average: 0.95, 1.01, 1.00
 14:29:19 up 6 days, 14:48,  5 users,  load average: 0.90, 0.97, 0.99
 14:30:19 up 6 days, 14:49,  5 users,  load average: 0.93, 0.96, 0.98
 14:31:19 up 6 days, 14:50,  5 users,  load average: 0.90, 0.94, 0.97
 14:32:20 up 6 days, 14:51,  5 users,  load average: 0.96, 0.95, 0.97
 14:33:20 up 6 days, 14:52,  5 users,  load average: 0.98, 0.95, 0.97
 14:34:20 up 6 days, 14:53,  5 users,  load average: 1.09, 0.99, 0.98
 14:35:20 up 6 days, 14:54,  5 users,  load average: 1.03, 0.99, 0.98
 14:36:20 up 6 days, 14:55,  5 users,  load average: 1.01, 0.99, 0.98
 14:37:20 up 6 days, 14:56,  5 users,  load average: 1.00, 0.99, 0.98
 14:38:21 up 6 days, 14:57,  5 users,  load average: 1.22, 1.05, 1.00
 14:39:21 up 6 days, 14:58,  5 users,  load average: 1.08, 1.04, 1.00
 14:40:21 up 6 days, 14:59,  5 users,  load average: 1.03, 1.03, 1.00
 14:41:21 up 6 days, 15:00,  5 users,  load average: 0.95, 1.01, 0.99
 14:42:21 up 6 days, 15:01,  5 users,  load average: 0.90, 0.97, 0.98
 14:43:21 up 6 days, 15:02,  5 users,  load average: 0.99, 0.99, 0.99
 14:44:22 up 6 days, 15:03,  5 users,  load average: 0.86, 0.94, 0.97
 14:45:22 up 6 days, 15:04,  5 users,  load average: 0.97, 0.95, 0.97
 14:46:22 up 6 days, 15:05,  5 users,  load average: 1.08, 0.99, 0.98
 14:47:22 up 6 days, 15:06,  5 users,  load average: 1.03, 0.99, 0.98
 14:48:22 up 6 days, 15:07,  5 users,  load average: 1.32, 1.07, 1.01

Perhaps the load average count could be run just before or in the middle of a second instead?

-- 
Simon Arlott


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