On 5/20/21 5:06 PM, Dietmar Eggemann wrote: > On 20/05/2021 14:38, Daniel Bristot de Oliveira wrote: >> On 5/20/21 12:33 PM, Quentin Perret wrote: >>> On Thursday 20 May 2021 at 11:16:41 (+0100), Will Deacon wrote: >>>> Ok, thanks for the insight. In which case, I'll go with what we discussed: >>>> require admission control to be disabled for sched_setattr() but allow >>>> execve() to a 32-bit task from a 64-bit deadline task with a warning (this >>>> is probably similar to CPU hotplug?). >>> >>> Still not sure that we can let execve go through ... It will break AC >>> all the same, so it should probably fail as well if AC is on IMO >>> >> >> If the cpumask of the 32-bit task is != of the 64-bit task that is executing it, >> the admission control needs to be re-executed, and it could fail. So I see this >> operation equivalent to sched_setaffinity(). This will likely be true for future >> schedulers that will allow arbitrary affinities (AC should run on affinity >> change, and could fail). >> >> I would vote with Juri: "I'd go with fail hard if AC is on, let it >> pass if AC is off (supposedly the user knows what to do)," (also hope nobody >> complains until we add better support for affinity, and use this as a motivation >> to get back on this front). >> >> -- Daniel > > (1) # chrt -d -T 5000000 -P 16666666 0 ./32bit_app > > (2) # ./32bit_app & > > # chrt -d -T 5000000 -P 16666666 -p 0 pid_of(32bit_app) > > > Wouldn't the behaviour of (1) and (2) be different w/o this patch? > > In (1) __sched_setscheduler() happens before execve so it operates on > p->cpus_ptr equal span. > > In (2) span != p->cpus_ptr so DL AC will fail. > As far as I got, the case (1) would be spitted in two steps: - __sched_setscheduler() will work, then - execv() would fail because (span != p->cpus_ptr) So... at the end, both (1) and (2) would result in a failure... am I missing something? -- Daniel
