Hi Michal,
On 1/27/25 10:10 PM, Michal Koutný Wrote:
Hello.
On Sat, Jan 25, 2025 at 01:25:12PM +0800, Abel Wu <wuyun.abel@xxxxxxxxxxxxx> wrote:
The per-task and per-cpu accounting have already been tracked by
t->sched_info.run_delay and rq->rq_sched_info.run_delay respectively.
Extends this to also include cgroups.
The PSI indicator, "some" of cpu.pressure, loses the insight into how
severely that cgroup is stalled. Say 100 tasks or just 1 task that gets
stalled at a certain point will show no difference in "some" pressure.
IOW "some" is a flat value that not weighted by the severity (e.g. # of
tasks).
IIUC below are three examples of when "some" tasks are waiting for CPU:
a)
t1 |----|
t2 |xx--|
b)
t1 |----|
t2 |x---|
t3 |-x--|
c)
t1 |----|
t2 |xx--|
t3 |xx--|
(- means runnable on CPU, x means runnable waiting on RQ)
Which pair from a), b), c) is indistinguishable via PSI? (Or can you
please add your illustrative example?)
PSI tracks stall times for each cpu, and
tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0)
which turns nr_delayed_tasks[cpu] into boolean value, hence loses
insight into how severely this task group is stalled on this cpu.
Thanks,
Abel
