Messages in this thread | | | Date | Wed, 30 Mar 2011 22:17:43 -0400 (EDT) | From | Len Brown <> | Subject | cpuidle asymmetry (was Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm) |
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> > > Maybe there is some other way to handle asymmetry ??
I mis-spoke on asymmetry.
Moorestown is already an example of an asymmetric system, since its deepest c-state is available on cpu0, but not on cpu1. So it needs different tables for each cpu.
I think what would work is a default c-state table for the system, and the ability of a per-cpu override table. I think that would gracefully handle the case of many identical cpus, and also systems with different tables per cpu.
The same goes for write-access to the tables. In the typical case, a single table can be shared for the entire system and nobody will be writing to it. However, with the governor changes to call dev->prepare and sift through all the states to find the legal one with the lowest power_usage... There is software today out of tree that updates that power_usage entry from prepare().
As I mentioned, I'm not fond of that mechanism - it looks racey to me. I'd rather see the capability of a drivers idle handler to demote to another handler in the driver and for the accounting to not get messed up when that happens. I think the way to do that is to let the driver do the accounting rather than doing it in the cpuidle caller.
cheers, -Len Brown, Intel Open Source Technology Center
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