On Fri, Mar 24, 2023 at 11:35:35PM +0100, Frederic Weisbecker wrote: > Le Sat, Mar 18, 2023 at 09:04:38AM +0100, Michal Hocko a écrit : > > On Fri 17-03-23 15:35:05, Marcelo Tosatti wrote: > > > On Fri, Mar 17, 2023 at 03:33:13PM -0300, Marcelo Tosatti wrote: > > > > On Fri, Mar 17, 2023 at 02:44:47PM +0100, Michal Hocko wrote: > > > > > From: Frederic Weisbecker <frederic@xxxxxxxxxx> > > > > > > > > > > Provide this new API to check if a CPU has been isolated either through > > > > > isolcpus= or nohz_full= kernel parameter. > > > > > > > > > > It aims at avoiding kernel load deemed to be safely spared on CPUs > > > > > running sensitive workload that can't bear any disturbance, such as > > > > > pcp cache draining. > > > > > > > > Hi Michal, > > > > > > > > This makes no sense to me. > > > > > > > > HK_TYPE_DOMAIN is set when isolcpus=domain is configured. > > > > HK_TYPE_TICK is set when nohz_full= is configured. > > > > > > > > The use-cases i am aware of use either: > > > > > > > > isolcpus=managed_irq,... nohz_full= > > > > OR > > > > isolcpus=domain,managed_irq,... nohz_full= > > > > > > > > So what is the point of this function again? > > > > > > > > Perhaps it made sense along with, but now does not make sense > > > > anymore: > > > > > > > > Subject: [PATCH 1/2] sched/isolation: Merge individual nohz_full features into a common housekeeping flag > > > > > > > > The individual isolation features turned on by nohz_full were initially > > > > split in order for each of them to be tunable through cpusets. However > > > > plans have changed in favour of an interface (be it cpusets or sysctl) > > > > grouping all these features to be turned on/off altogether. Then should > > > > the need ever arise, the interface can still be expanded to handle the > > > > individual isolation features. > > > > > > > > But Michal can just use housekeeping_test_cpu(cpu, HK_TYPE_TICK) and > > > > the convertion of nohz_full features into a common housekeeping flag > > > > can convert that to something else later? > > > > > > Actually introducing cpu_is_isolated() seems fine, but it can call > > > housekeeping_test_cpu(cpu, HK_TYPE_TICK) AFAICS. > > > > This is not really my area. Frederic, could you have a look please? > > The point is to have a function that tells if either nohz_full= or > isolcpus=[domain] has been passed for the given CPU. > > Because I assumed that both would be interested in avoiding that flush > noise, wouldn't it be the case? Yes, that is the case. But as a note: for the two main types of configuration performed (one uses isolcpus=[domain] and the other cgroups, for isolating processes) nohz_full= is always set. So just testing for nohz_full= would be sufficient (which perhaps would make the code simpler).
