Messages in this thread | | | Subject | Higer latency with dynamic tick (need for an io-ondemand govenor?) | Date | Fri, 18 Apr 2008 10:43:32 -0500 | From | "Woodruff, Richard" <> |
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Hi,
When capturing some traces with dynamic tick we were noticing the interrupt latency seems to go up a good amount. If you look at the trace the gpio IRQ is now offset a good amount. Good news I guess is its pretty predictable.
* If we couple this with progressively higher latency C-States we see that IO speed can fall by a good amount, especially for PIO mixes. Now if QOS is maintained you may or may-not care.
I was wondering what thoughts of optimizing this might be.
One thought was if an io-ondemand of some sort was used. It could track interrupt statistics and be feed back into cpu-idle. When there is a high interrupt load period it could shrink the acceptable latency and thus help choose a good a C-State which favors throughput. Some moving average window could be used to track it.
Perhaps a new interrupt attribute could be attached at irq request time to allow the tracking of bandwidth important devices.
The attached is captured on a .22 kernel. The same should be available in a bit on a .24 kernel.
Regards, Richard W.
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