On Mon, Jul 19, 2021 at 03:26:49PM +0200, Frederic Weisbecker wrote: > On Wed, Jul 14, 2021 at 01:31:57PM -0300, Marcelo Tosatti wrote: > > On Wed, Jul 14, 2021 at 03:54:20PM +0200, Frederic Weisbecker wrote: > > > Add a new cpuset.isolation_mask file in order to be able to modify the > > > housekeeping cpumask for each individual isolation feature on runtime. > > > In the future this will include nohz_full, unbound timers, > > > unbound workqueues, unbound kthreads, managed irqs, etc... > > > > > > Start with supporting domain exclusion and CPUs passed through > > > "isolcpus=". > > > > It is possible to just add return -ENOTSUPPORTED for the features > > whose support is not present? > > Maybe, although that looks like a specialized error for corner cases. Well, are you going to implement runtime enablement for all features, including nohz_full, in the first patch set? >From my POV returning -ENOTSUPPORTED would allow for a gradual implementation of the features. > > > CHECKME: Should we have individual cpuset.isolation.$feature files for > > > each isolation feature instead of a single mask file? > > > > Yes, guess that is useful, for example due to the -ENOTSUPPORTED > > comment above. > > > > > > Guarantees on updates > > ===================== > > > > Perhaps start with a document with: > > > > On return to the write to the cpumask file, what are the guarantees? > > > > For example, for kthread it is that any kernel threads from that point > > on should start with the new mask. Therefore userspace should > > respect the order: > > > > 1) Change kthread mask. > > 2) Move threads. > > > > Yep. > > > Updates to interface > > ==================== > > > > Also, thinking about updates to the interface (which today are one > > cpumask per isolation feature) might be useful. What can happen: > > > > 1) New isolation feature is added, feature name added to the interface. > > > > Userspace must support new filename. If not there, then thats an > > old kernel without support for it. > > > > 2) If an isolation feature is removed, a file will be gone. What should > > be the behaviour there? Remove the file? (userspace should probably > > ignore the failure in that case?) (then features names should not be > > reused, as that can confuse #1 above). > > Heh, yeah that's complicated. I guess we should use one flag per file as that > fits well within the current cpuset design. But we must carefully choose the new > files to make sure they have the least chances to be useless in the long term. > > > Or maybe have a versioned scheme? > > I suspect we should avoid that at all costs :-) > > Thanks! Makes sense.
