On 04/18/2010 03:03 PM, Arjan van de Ven wrote:
From 27966bedabea83c4f3ae77507eceb746b1f6ebae Mon Sep 17 00:00:00 2001 From: Arjan van de Ven<arjan@xxxxxxxxxxxxxxx> Date: Sun, 18 Apr 2010 11:15:56 -0700 Subject: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO The ondemand cpufreq governor uses CPU busy time (e.g. not-idle time) as a measure for scaling the CPU frequency up or down. If the CPU is busy, the CPU frequency scales up, if it's idle, the CPU frequency scales down. Effectively, it uses the CPU busy time as proxy variable for the more nebulous "how critical is performance right now" question. This algorithm falls flat on its face in the light of workloads where you're alternatingly disk and CPU bound, such as the ever popular "git grep", but also things like startup of programs and maildir using email clients... much to the chagarin of Andrew Morton. This patch changes the ondemand algorithm to count iowait time as busy, not idle, time. As shown in the breakdown cases above, iowait is performance critical often, and by counting iowait, the proxy variable becomes a more accurate representation of the "how critical is performance" question. The problem and fix are both verified with the "perf timechar" tool. Signed-off-by: Arjan van de Ven<arjan@xxxxxxxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
