Re: [regression] cpuset: offlined CPUs removed from affinity masks

[Tejun Heo]

On Wed, Feb 19, 2020 at 10:43:05AM -0500, Mathieu Desnoyers wrote:
> The regression I'm talking about here is that CONFIG_CPUSET=y changes the
> behavior of the sched_setaffinify system call, which existed prior to
> cpusets.
> 
> sched_setaffinity should behave in the same way for kernels configured with
> CONFIG_CPUSET=y or CONFIG_CPUSET=n.
> 
> The fact that cpuset decides to irreversibly change the task affinity mask
> may not be considered a regression if it has always done that, but changing
> the behavior of sched_setaffinity seems to fit the definition of a regression.

We generally use "regression" for breakages which weren't in past
versions but then appeared later. It has debugging implications
because if we know something is a regression, we generally can point
to the commit which introduced the bug either through examining the
history or bisection.

It is a silly bug, for sure, but slapping regression name on it just
confuses rather than helping anything.

-- 
tejun