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SubjectRe: RFC: Link Time Optimization support for the kernel

* Andi Kleen <andi@firstfloor.org> wrote:

> This rather large patchkit enables gcc Link Time Optimization (LTO)
> support for the kernel.
>
> With LTO gcc will do whole program optimizations for
> the whole kernel and each module. This increases compile time,
> but can generate faster code.

By how much does it increase compile time?

How much faster does kernel code get?

Last time I checked LTO optimizations (half a year ago) it
resulted in significantly slower build times.

I tried out and measured the LTO speedups and was less than
impressed by them - a lot of build time increase for not much
increase in performance. There was also visible, ongoing
maintenance cost.

The combination of these seemed like a show-stopper.

It's obviously an optimization feature we should consider, but
we really need hard numbers to make a cost/benefit analysis.

Thanks,

Ingo


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