Messages in this thread | | | Date | Tue, 29 Jul 2008 18:31:13 +0200 | From | Andi Kleen <> | Subject | Re: BUG: unable to handle kernel NULL pointer dereference at 00000002 |
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> > A power saving feature that has a significant trade off between power > > and performance. > > do you have numbers to explain "significant tradeoff" ?
I don't have numbers, but from the theory it seems pretty clear. When you e.g. have two processes with 6MB cache foot print and you have two 2C CPUs with 6MB cache they will fit in cache, but with power aware scheduler they won't because both processes will run on the single 6MB package. With NUMA the effect is even worse because also the memory controllers are not used evenly. And there's the FSB bandwidth, but that's a secondary issue. > > > > This means performance will go down. Perhaps it would be ok on > > battery, > > the illusion that power only matters on battery got buried a few years > ago ;)
My understanding was always that unless you're on battery power saving features that are enabled by default are not supposed to impact performance significantly. When the user says impacting performance is ok then doing that is fine of course, but not by default. And I don't think that's an illusion. In fact if power saving means losing a lot of performance people would get discouraged from using it, and surely you don't want that.
-Andi
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