Subject: Re: [PATCH 06/22] kbuild: lto: limit inlining

From: Sami Tolvanen <[email-masked]>
Date: Wed, 24 Jun 2020 16:37:24 -0700

On Wed, Jun 24, 2020 at 11:20:55PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 24, 2020 at 01:31:44PM -0700, Sami Tolvanen wrote:
> > This change limits function inlining across translation unit
> > boundaries in order to reduce the binary size with LTO.
> > 
> > The -import-instr-limit flag defines a size limit, as the number
> > of LLVM IR instructions, for importing functions from other TUs.
> > The default value is 100, and decreasing it to 5 reduces the size
> > of a stripped arm64 defconfig vmlinux by 11%.
> 
> Is that also the right number for x86? What about the effect on
> performance? What did 6 do? or 4?

This is the size limit we decided on for Android after testing on
arm64, but the number is obviously a compromise between code size
and performance. I'd be happy to benchmark this further once other
concerns have been resolved.

Sami

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