On Thu, 5 Nov 2020 at 19:24, Pavel Machek pavel@ucw.cz wrote:
Hi!
From: Joel Stanley joel@jms.id.au
commit a02f6d42357acf6e5de6ffc728e6e77faf3ad217 upstream.
It's not done anything for a long time. Save the percpu variable, and emit a warning to remind users to not expect it to do anything.
This uses pr_warn_once instead of pr_warn_ratelimit as testing 'ppc64_cpu --smt=off' on a 24 core / 4 SMT system showed the warning to be noisy, as the online/offline loop is slow.
I don't believe this is good idea for stable. It is in 5.9-rc2, and likely mainline users will get userspace fixed, but that warning is less useful for -stable users.
The warning is about the existing behaviour of the kernel. It does let the user know that they won't see any difference in behaviour when tweaking the smt_snooze_delay variable, which was a real issue that Anton hit.
I agree that the future commit that removes smt_snooze_delay from the kernel should not be backported.
Cheers,
Joel
(And besides, it does not fix any serious bug).
Best regards, Pavel