Re: [PATCH v2] net: raise RCU qs after each threaded NAPI poll

[Yan Zhai <yan@cloudflare.com>]

Hi Eric,

On Fri, Mar 1, 2024 at 2:30 AM Eric Dumazet <edumazet@google.com> wrote:
>
> I could not see the reason for 1sec (HZ) delays.
>
> Would calling rcu_softirq_qs() every ~10ms instead be a serious issue ?
>
The trouble scenarios are often when we need to detach an ad-hoc BPF
tracing program, or restart a monitoring service. It is fine as long
as they do not block for 10+ seconds or even completely stall under
heavy traffic. Raising a QS every few ms or HZ both work in such
cases.

> In anycase, if this all about rcu_tasks, I would prefer using a macro
> defined in kernel/rcu/tasks.h
> instead of having a hidden constant in a networking core function.

Paul E. McKenney was suggesting either current form or

         local_bh_enable();
         if (!IS_ENABLED(CONFIG_PREEMPT_RT))
                 rcu_softirq_qs_enable(local_bh_enable());
         else
                 local_bh_enable();

With an interval it might have to be
"rcu_softirq_qs_enable(local_bh_enable(), &next_qs);" to avoid an
unnecessary extern/static var. Will it make more sense to you?

thanks

>
> Thanks.