Hi,
On 03/09/25 11:33, Andrea Righi wrote:
> From: Joel Fernandes <joelagnelf@xxxxxxxxxx>
>
> Hotplugged CPUs coming online do an enqueue but are not a part of any
> root domain containing cpu_active() CPUs. So in this case, don't mess
> with accounting and we can retry later. Without this patch, we see
> crashes with sched_ext selftest's hotplug test due to divide by zero.
>
> Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
> ---
> kernel/sched/deadline.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 3c478a1b2890d..753e50b1e86fc 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1689,7 +1689,12 @@ int dl_server_apply_params(struct sched_dl_entity *dl_se, u64 runtime, u64 perio
> cpus = dl_bw_cpus(cpu);
> cap = dl_bw_capacity(cpu);
>
> - if (__dl_overflow(dl_b, cap, old_bw, new_bw))
> + /*
> + * Hotplugged CPUs coming online do an enqueue but are not a part of any
> + * root domain containing cpu_active() CPUs. So in this case, don't mess
> + * with accounting and we can retry later.
> + */
> + if (!cpus || __dl_overflow(dl_b, cap, old_bw, new_bw))
> return -EBUSY;
>
> if (init) {
Yuri is proposing to ignore dl-servers bandwidth contribution from
admission control (as they essentially operate on the remaining
bandwidth portion not available to RT/DEADLINE tasks):
https://lore.kernel.org/lkml/20250903114448.664452-1-yurand2000@xxxxxxxxx/
His patch should make this patch not required. Would you be able and
willing to test this assumption?
I don't believe Peter already expressed his opinion on what Yuri is
proposing, so this might be moot. But if we go that way all dl-servers
should share that non-RT portion of bandwidth I would guess. And we will
need to probably add checks and subdivide among active dl-servers, don't
we? Peter, others, what do you think?
Thanks,
Juri
