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    SubjectRe: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO
    Hi!

    > 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.

    Well, and now, if you do something like cat /dev/<your usb1.1 hdd> >
    /dev/null, you'll keep cpu on max frequency. Not a problem for new
    core i7, but probably big deal for athlon 64.

    Maybe modern cpus can and should simply react faster?

    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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