Re: [PATCH v2 0/4] riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

Palmer Dabbelt
2023-06-21T18:19:41Z

On Wed, 21 Jun 2023 10:51:15 PDT (-0700), bjorn@kernel.org wrote:
> Conor Dooley <conor@kernel.org> writes:
>
> [...]
>
>>> So I'm no longer actually sure there's a hang, just something slow.
>>> That's even more of a grey area, but I think it's sane to call a 1-hour
>>> link time a regression -- unless it's expected that this is just very
>>> slow to link?
>>
>> I dunno, if it was only a thing for allyesconfig, then whatever - but
>> it's gonna significantly increase build times for any large kernels if LLD
>> is this much slower than LD. Regression in my book.
>>
>> I'm gonna go and experiment with mixed toolchain builds, I'll report
>> back..
>
> I took palmer/for-next (1bd2963b2175 ("Merge patch series "riscv: enable
> HAVE_LD_DEAD_CODE_DATA_ELIMINATION"")) for a tuxmake build with llvm-16:
>
> | ~/src/tuxmake/run -v --wrapper ccache --target-arch riscv \
> | --toolchain=llvm-16 --runtime docker --directory . -k \
> | allyesconfig
>
> Took forever, but passed after 2.5h.

Thanks. I just re-ran mine 17/trunk LLD under time (rather that just
checking top sometimes), it's at 1.5h but even that seems quite long.

I guess this is sort of up to the LLVM folks: if it's expected that DCE
takes a very long time to link then I'm not opposed to allowing it, but
if this is probably a bug in LLD then it seems best to turn it off until
we sort things out over there.

I think maybe Nick or Nathan is the best bet to know?

> CONFIG_CC_VERSION_TEXT="Debian clang version 16.0.6 (++20230610113307+7cbf1a259152-1~exp1~20230610233402.106)"
>
>
> Björn