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Re: [PATCH 0/5] tcg: Dynamically allocate temporaries

From: BALATON Zoltan
Subject: Re: [PATCH 0/5] tcg: Dynamically allocate temporaries
Date: Wed, 20 Jan 2021 00:06:16 +0100 (CET)

On Tue, 19 Jan 2021, Richard Henderson wrote:
My recent change for caching tcg constants has, in a number of cases,
overflowed the statically allocated array of temporaries.  Change to
dynamic allocation.

This seems to work for me so

Tested-by: BALATON Zoltan <balaton@eik.bme.hu>

but have you done any performance tests to check that this actually improves emulation speed? To mee it seems slower. Booting AmigaOS on sam460ex with c0dd6654f207 (just before your TCG series) takes:

real    0m33.829s
user    0m34.432s
sys     0m0.296s

but on HEAD with this series:

real    0m44.381s
user    0m46.058s
sys     0m0.532s

This is noticable decrease in speed also without measuring it. With just increasing the TCG_MAX_TEMPS to 2048 on 7c79721606be without this series I get:

real    0m42.681s
user    0m44.208s
sys     0m0.435s

So the performance regression is somewhere in the original series not in this fix up series.

I'll note that nothing in check-acceptance triggers this overflow.
Anyone care to add some more test cases there?

The proposed test for the upcoming pegasos2 machine may also catch this (when that will be merged, its dependencies are still under review) or the sam460ex test that currently only checks the firmware could be enhanced to try to boot AROS if somebody wants to do that. The drawback is that it needs an external iso whereas the current test doesn't need any additional images but it did not catch problems with IRQ and neither this problem with TCG temps. This problem was also found with riscv and mips I think but don't know if those would be easier to test.


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