RFR: 8318364: Add an FFM-based implementation of harfbuzz OpenType layout [v4]

[Phil Race]

On Mon, 6 Nov 2023 23:58:11 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

> > So we have somewhere around a fixed 125ms startup cost for the FFM case - as measured on my Mac,
> > but only 35-40ms of that is attributable to the specific needs of layout.
> 
> That looks unfortunate. I guess if we will start to use ffm in other places we can easily spend of 1 second budget on startup=(

Yes, this case is sufficiently uncommon, that it is OK, and is a decent way to help us track improvements to FFM.
But it would be another matter to have to do it for however many of our core software loops and AWT window
manager interaction calls we need to get running for a minimal app.

> 
> > layoutCnt=16000 total=193ms <<< app fully displayed
> > vs
> > layoutCnt=16000 total=453ms <<< app fully displayed
> 
> It looks strange that 16000 calls are not enough to warmup, and the difference is so large.

I am not a C2 expert, (not even an amateur), I just assume that it takes a lot of calls to be fully optimized.

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PR Comment: https://git.openjdk.org/jdk/pull/15476#issuecomment-1797086938