Buildworld and buildkernel with very slow compilation, recently

[Dimitry Andric]

On 21 Jun 2020, at 14:36, Chris Nehren <cnehren at pobox.com> wrote:
> 
> On Sunday, June 21, 2020 8:11:15 AM EDT Michael Grimm wrote:
>> Hi,
>> 
>> I am following FreeBSD 12.1-STABLE.
>> 
>> Clang has been upgraded to version 10.0.0 on May, 1st, and ever since that
>> time, I do observe a dramatic increase in compilation times of building
>> world, kernel and ports. I didn't benchmark the exact times, but
>> compilation times are at least increased by a factor of 1.5. Nothing has
>> changed of the last month besides upgrading 12.1-Stable every other week.
>> 
>> Has anyone else been bitten by this?
> 
> I don't have measurements to corroborate this, but here's a mailing list
> thread where folks are talking about it (split across two URLs, the OP posted
> in April and then there was a followup in May):
> 
> http://lists.llvm.org/pipermail/llvm-dev/2020-April/140938.html
> https://lists.llvm.org/pipermail/llvm-dev/2020-May/141482.html
> 
> So there definitely seems to be *something* going on, and you are indeed not
> crazy. :)

Indeed, there is some upstream discussion going on about this issue.
There are some scenarios where people see non-negligible performance
loss, but apparently not everybody suffers from it. If you build the
whole ports collection, it is rather likely you may bump into it. I have
personally not seen much performance difference in building world,
kernel etc.

One of the upstream problems is that there is not really any
authoritative performance regression log being built up, so it is hard
to see where such regressions were introduced. Somebody then has to
spend a lot of time tracking down each and every regression, and then
attempt to untangle it from the dozens of commits made around the same
time. :)

In any case, there is at least some attention on it now, so hopefully
this will improve again. I don't think such fixes will be trivial
though, so it is not likely they will land in 10.0.1.

-Dimitry

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