Messages in this thread | | | Date | Sun, 22 Feb 2015 09:22:28 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs |
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* Ingo Molnar <mingo@kernel.org> wrote:
> - Do you have enough RAM that there's essentially no IO > in the system worth speaking of? Do you have enough RAM > to copy a whole kernel tree to /tmp/linux/ and do the > measurement there, on ramfs?
Doing that will also pin down the page cache: kernel build times are very sensitive to the page cache layout, and once a page cache layout is established on systems with lots of RAM it does not tend to be flushed out. But the next bootup will generate another random page cache layout - which makes inter-kernel kernel build times comparisons much noiser than the run-to-run numbers suggest.
So to get more precise measurements a 'pinned' page cache layout and the dynamic debug switch you implemented is very helpful and --repeat stddev will be pretty representative of the true noise of the measurement.
Thanks,
Ingo
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