On Tue, 14 Dec 2021, Marcelo Tosatti wrote: > > downside is that there will be a performance penalty if an application > > running on a NOHZ_FULL CPU is page allocator intensive for whatever > > reason. However, I guess this is unlikely because if there was a lot > > of kernel activity for a NOHZ_FULL CPU, the vmstat shepherd would also > > cause interference. > > Yes, it does, and its being fixed: > > https://lkml.org/lkml/2021/12/8/663 > > Honestly i am not sure whether the association between a nohz_full CPU > and "should be mostly in userspace" is desired. The RCU solution > would be more generic. As Nicolas mentioned, for the usecases in > questions, either solution is OK. > > Thomas, Frederic, Christoph, do you have any opinion on this ? Applications running would ideally have no performance penalty and there is no issue with kernel activity unless the application is in its special low latency loop. NOHZ is currently only activated after spinning in that loop for 2 seconds or so. Would be best to be able to trigger that manually somehow. And I would prefer to be able to run the whole system as NOHZ and have the ability to selectively enable the quiet mode if a process requires it for its processing.
