Messages in this thread | | | Date | Mon, 9 Sep 2019 11:59:51 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH 2/2] sched/debug: add sched_update_nr_running tracepoint |
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On 09/04/19 19:48, Peter Zijlstra wrote: > On Wed, Sep 04, 2019 at 03:37:11PM +0100, Qais Yousef wrote: > > > I managed to hook into sched_switch to get the nr_running of cfs tasks via > > eBPF. > > > > ``` > > int on_switch(struct sched_switch_args *args) { > > struct task_struct *prev = (struct task_struct *)bpf_get_current_task(); > > struct cgroup *prev_cgroup = prev->cgroups->subsys[cpuset_cgrp_id]->cgroup; > > const char *prev_cgroup_name = prev_cgroup->kn->name; > > > > if (prev_cgroup->kn->parent) { > > bpf_trace_printk("sched_switch_ext: nr_running=%d prev_cgroup=%s\\n", > > prev->se.cfs_rq->nr_running, > > prev_cgroup_name); > > } else { > > bpf_trace_printk("sched_switch_ext: nr_running=%d prev_cgroup=/\\n", > > prev->se.cfs_rq->nr_running); > > } > > return 0; > > }; > > ``` > > > > You can do something similar by attaching to the sched_switch tracepoint from > > a module and a create a new event to get the nr_running. > > > > Now this is not as accurate as your proposed new tracepoint in terms where you > > sample nr_running, but should be good enough? > > The above is after deactivate() and gives an up-to-date count for > decrements. Attach something to trace_sched_wakeup() to get the > increment update.
I just remembered that sched_switch and sched_wakeup aren't EXPORT_TRACEPOINT*() so can't be attached to via out of tree module. But still accessible via eBPF.
There has been several attempts to export these tracepoints but they were NACKed because there was no in-kernel module that needed them.
https://lore.kernel.org/lkml/20150422130052.4996e231@gandalf.local.home/
-- Qais Yousef
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