Hello,
On Tue, Nov 28, 2023 at 01:32:53PM -0500, Waiman Long wrote:
> On 11/28/23 11:56, Tejun Heo wrote:
> > Hello,
> >
> > On Sun, Nov 26, 2023 at 11:19:56PM -0500, Waiman Long wrote:
> > > +bool cpuset_cpu_is_isolated(int cpu)
> > > +{
> > > + unsigned int seq;
> > > + bool ret;
> > > +
> > > + do {
> > > + seq = read_seqcount_begin(&isolcpus_seq);
> > > + ret = cpumask_test_cpu(cpu, isolated_cpus);
> > > + } while (read_seqcount_retry(&isolcpus_seq, seq));
> > > + return ret;
> > > +}
> > > +EXPORT_SYMBOL_GPL(cpuset_cpu_is_isolated);
> > We're testing a bit in a bitmask. I don't think we need to worry about value
> > integrity from RMW updates being broken up. ie. We can just test the bit
> > without seqlock and drop the first patch?
>
> My concern is that if we have an isolated partition with a set of isolated
> CPUs (say 2-4), I don't want any addition, deletion of changes made to
> another isolated partition affects the test of the pre-existing one. Testing
> result of the partition being change is fair game.
>
> Depending on how the cpumask operators are implemented, we may not have a
> guarantee that testing CPU 2, for instance, will always return true. That is
Can you please elaborate this part a bit? I'm having a difficult time
imagining the sequence of operations where this would matter but that could
easily be me not being familiar with the details.
Thanks.
--
tejun
