From 60c27fb59f6cffa73fc8c60e3a22323c78044576 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 18 Jun 2024 10:09:20 -1000 Subject: sched_ext: Implement sched_ext_ops.cpu_online/offline() Add ops.cpu_online/offline() which are invoked when CPUs come online and offline respectively. As the enqueue path already automatically bypasses tasks to the local dsq on a deactivated CPU, BPF schedulers are guaranteed to see tasks only on CPUs which are between online() and offline(). If the BPF scheduler doesn't implement ops.cpu_online/offline(), the scheduler is automatically exited with SCX_ECODE_RESTART | SCX_ECODE_RSN_HOTPLUG. Userspace can implement CPU hotpplug support trivially by simply reinitializing and reloading the scheduler. scx_qmap is updated to print out online CPUs on hotplug events. Other schedulers are updated to restart based on ecode. v3: - The previous implementation added @reason to sched_class.rq_on/offline() to distinguish between CPU hotplug events and topology updates. This was buggy and fragile as the methods are skipped if the current state equals the target state. Instead, add scx_rq_[de]activate() which are directly called from sched_cpu_de/activate(). This also allows ops.cpu_on/offline() to sleep which can be useful. - ops.dispatch() could be called on a CPU that the BPF scheduler was told to be offline. The dispatch patch is updated to bypass in such cases. v2: - To accommodate lock ordering change between scx_cgroup_rwsem and cpus_read_lock(), CPU hotplug operations are put into its own SCX_OPI block and enabled eariler during scx_ope_enable() so that cpus_read_lock() can be dropped before acquiring scx_cgroup_rwsem. - Auto exit with ECODE added. Signed-off-by: Tejun Heo Reviewed-by: David Vernet Acked-by: Josh Don Acked-by: Hao Luo Acked-by: Barret Rhoden --- tools/sched_ext/scx_qmap.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'tools/sched_ext/scx_qmap.c') diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c index 2a97421afe9a..920fb54f9c77 100644 --- a/tools/sched_ext/scx_qmap.c +++ b/tools/sched_ext/scx_qmap.c @@ -122,5 +122,9 @@ int main(int argc, char **argv) bpf_link__destroy(link); UEI_REPORT(skel, uei); scx_qmap__destroy(skel); + /* + * scx_qmap implements ops.cpu_on/offline() and doesn't need to restart + * on CPU hotplug events. + */ return 0; } -- cgit v1.2.3