[Bug 221029] AMD Ryzen: strange compilation failures using poudriere or plain buildkernel/buildworld

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=221029

--- Comment #45 from Don Lewis <truckman at FreeBSD.org> ---
I've never seen a successful amd64 ghc build.  i386, no problem.

I don't recall seeing that assert before, but it could have been hiding in the
weeds.  It is strangely consistent, though.

One difference between my buildworld/buildkernel results, which were fairly
good, and my poudriere runs, which had more fallout is that the latter have a
much larger memory footprint.  The machine I'm testing has 64GB of RAM, with
tons free during the buildworld/buildkernel test, even with tmpfs.  On the
other hand, when I'm running poudriere with tmpfs, there is a lot of memory
pressure and the machine starts using swap.  I'm wondering if page fault
exceptions sometimes get mis-reported or reported somewhat differently than
older CPUs, causing us to misinterpret them has hard sigsegv faults.  This fits
the Linux symptoms, especially the bash segfaults.  If libtool is being used,
then the bash process for each libtool execution will sit and wait for the
compiler process that it spawed to finish.  In the meantime, the memmory used
by bash will be idle is is likely to get paged out.  After the compiler exits
and bash restarts, it is likely to experience a number of page faults.

Now that the system hang/crash problem is fixed for me, which accounted for
many of the earlier failures that I saw, and which was not sensitive to SMT, or
clock speed, I'm going to go back to some underclocking tests with SMT disabled
to see if that has any effect when building ports.

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