Messages in this thread | | | Date | Tue, 20 Apr 2010 04:07:08 -0700 | From | Arjan van de Ven <> | Subject | Re: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO |
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On Tue, 20 Apr 2010 11:29:02 +0200 Thomas Renninger <trenn@suse.de> wrote:
> Have you looked at: > /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_transition_latency > and > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/sampling_rate > Transition latency comes from ACPI tables and sampling rate depends > on it.
of course I have; in practice on systems i use it is always a 10 milliseconds interval, which is the minimum it gets. Yes this was a bug, no it wasn't the bug here ;-)
> Reducing the sampling rate, significantly reduces performance loss
while it does, it is not nearly sufficient for the alternating IO/CPU cases I've looked at. I've looked at many timecharts for various IO/CPU workloads, including my normal own use as well as Andrews and the CPU busy periods are in the 1 - 20 msec range between IOs most of the time, for which a 10 msec sampling is obviously problematic.
-- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org
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