linux-kernel - [PATCH] Optimize calc

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Message-Id: <200612111450.07722.dada1@cosmosbay.com>
Date:	Mon, 11 Dec 2006 14:50:07 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] Optimize calc_load()

calc_load() is called by timer interrupt to update avenrun[].
It currently calls nr_active() at each timer tick (HZ per second), while the 
update of avenrun[] is done only once every 5 seconds. (LOAD_FREQ=5 Hz)

nr_active() is quite expensive on SMP machines, since it has to sum up 
nr_running and nr_uninterruptible of all online CPUS, bringing foreign dirty 
cache lines.

This patch is an optimization of calc_load() so that nr_active() is called 
only if we need it.

The use of unlikely() is welcome since the condition is true only once every 
5*HZ time.

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>

View attachment "calc_load.patch" of type "text/plain" (821 bytes)