Re: [PATCH RFC 10/10] tests/migration-tests: Add test case for responsive CPU throttle

[Fabiano Rosas <farosas@suse.de>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On Thu, 12 Sept 2024 at 14:48, Fabiano Rosas <farosas@suse.de> wrote:
>> Peter Maydell <peter.maydell@linaro.org> writes:
>> > For some examples from this week:
>> >
>> > https://gitlab.com/qemu-project/qemu/-/jobs/7802183144
>> > https://gitlab.com/qemu-project/qemu/-/jobs/7799842373
>> > https://gitlab.com/qemu-project/qemu/-/jobs/7786579152
>> > https://gitlab.com/qemu-project/qemu/-/jobs/7786579155
>>
>> About these:
>>
>> There are 2 instances of plain-old-SIGSEGV here. Both happen in
>> non-x86_64 runs and on the /multifd/tcp/plain/cancel test, which means
>> they're either races or memory ordering issues. Having i386 crashing
>> points to the former. So having the CI loaded and causing timeouts is
>> probably what exposed the issue.
>
> They're also both TCI. Would these tests be relying on
> specific atomic-access behaviour in the guest code that's
> running, or is all the avoidance-of-races in the migration
> code in QEMU itself?

I misspoke about memory ordering, this is all just the x86 host and the
multifd threads in QEMU having synchronization issues.

>
> (I don't know of any particular problems with TCI's
> implementation of atomic accesses, so this is just a stab
> in the dark.)
>
> thanks
> -- PMM