Linux kernel cgroup v2 CFS - CPU throttled_usec accounting?

[Costa Shulyupin]

On Sat, 11 Jan 2025 at 13:29, Alexandru Lazarev
<alexandru.lazarev at gmail.com> wrote:
> In Linux kernel cgroup v2’s CFS scheduler, how is cpu.max throttled_usec accounted when a cgroup with multiple threads gets throttled during a single quota period? Specifically, is throttled_usec tracked as the total wall-clock time that the cgroup was throttled as a whole, or is it a sum of the throttled times of all individual threads?
>
> Kernel Version: "5.14.0-284.11.1.el9_2.x86_64 #1 SMP PREEMPT_DYNAMIC Tue May 9 11:41:53 PDT 2023 x86_64 x86_64 x86_64 GNU/Linux" Distro: Oracle Linux 9.x

Hi

When the cgroup is throttled, all tasks (threads) within the cgroup
are simultaneously prevented from running. The `throttled_time`
counter starts incrementing when the cgroup as a whole enters the
throttled state and stops when the cgroup is no longer throttled.

Quote:

"throttled_time: The total time duration (in nanoseconds) for which
entities of the group have been throttled."

  https://docs.kernel.org/scheduler/sched-bwc.html#:~:text=throttled_time

The source:

void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
{
        ...
        cfs_b->throttled_time += rq_clock(rq) - cfs_rq->throttled_clock;
        ...

static int cpu_extra_stat_show(struct seq_file *sf, struct
cgroup_subsys_state *css)
{
        struct task_group *tg = css_tg(css);
        struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
        ...
        throttled_usec = cfs_b->throttled_time;

Costa
Thanks