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Yes, but only as a side effect, and the patch should not rely on it. dl_bw_gen changes in a rebuild, which holds cpuset_mutex. From patch 18 on, set_cpus_allowed_dl() reaches this test only from cpuset_attach(), which holds cpuset_mutex too. At this patch, from reading, other callers still reach it without cpuset_mutex: select_fallback_rq(), and sched_setaffinity() with admission control off. A rebuild can then change dl_bw_gen between the test and the __dl_sub(). The planned next version takes dl_departed_lock around the test and the update of the record, from this patch on. > > + * enters the class. A runtime below about a millionth of the period > > + * gives a bandwidth of 0. It counts for nothing, and no move updates > > Ah right, quite cryptic corner case buried in this comment. :) > > This is the 1024ns/2s of the test. Which indeed gets dl_bw 0. Don't > think it's a huge deal from a theory/practice pov as to actually make an > impact we probably need quite a lot of these admitted (fork bomb style). > But it's still weird :P. Not sure if we want to impose a min of 1 dl_bw > for these. If it actually complicates the accounting (for no good > returns) or not. I agree that it is odd. I left it as it is upstream. The accounting needs no special case for it beyond this comment: a bandwidth of 0 is added and removed like any other. The case move_zero_bw of deadline_bw_test covers it. A minimum of 1 would change what sched_setattr() admits, by one millionth of a CPU for each such task. I would rather not do that in a series of fixes. I can send it as a separate patch afterwards if you want it. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com