Re: [PATCH] sched_ext: Documentation: add note about multiple ops.enqueue() calls in a row

Cheng-Yang Chou
2026-04-20T15:24:03Z

Hi Kuba,

On Mon, Apr 20, 2026 at 03:21:59PM +0000, Kuba Piecuch wrote:
> Hi Cheng-Yang,
>
> On Mon Apr 20, 2026 at 3:12 PM UTC, Cheng-Yang Chou wrote:
> > Hi Kuba,
> >
> > On Mon, Apr 20, 2026 at 02:39:39PM +0000, Kuba Piecuch wrote:
> >> Commit 84b1a0ea0b7c
> >> ("sched_ext: Implement scx_bpf_dsq_reenq() for user DSQs")
> >> introduced the possibility of ops.enqueue() being called multiple times
> >> in a row for the same task without intervening calls to ops.dequeue().
> >> AFAIK this was not possible before that commit.
> > ^^^^^
> > Nit: Do we really need this line in the commit message?
> > Perhaps we can just drop this?
>
> I put it there just in case someone was actually aware of a scenario before
> that commit where we can have multiple ops.enqueue() calls in a row.

I see, thanks!

>
> Regarding removing the line: yeah, I guess it's a bit redundant.
> I'll send a v2.
>
> >
> >> Document this behavior as it may be surprising to some.
> >>
> >> Signed-off-by: Kuba Piecuch <jpiecuch@google.com>
> >> ---
> >> Documentation/scheduler/sched-ext.rst | 5 +++++
> >> 1 file changed, 5 insertions(+)
> >>
> >> diff --git a/Documentation/scheduler/sched-ext.rst b/Documentation/scheduler/sched-ext.rst
> >> index 03d595d178ea..fba09aa1cd4e 100644
> >> --- a/Documentation/scheduler/sched-ext.rst
> >> +++ b/Documentation/scheduler/sched-ext.rst
> >> @@ -339,6 +339,11 @@ The following briefly shows how a waking task is scheduled and executed.
> >> leaves (e.g., when ``ops.dispatch()`` moves it to a terminal DSQ, or
> >> on property change / sleep).
> >>
> >> + Note that ``ops.enqueue()`` can be called multiple times in a row without
> >> + an intervening call to ``ops.dequeue()``. This can happen, for example,
> >> + when a task on a user-created DSQ is re-enqueued using
> >> + ``scx_bpf_dsq_reenq()``. The task stays in BPF custody the entire time.
> >> +
> >
> > Thanks for adding and clarifying this. ^v^
> >
> > Acked-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
> >
>
> Thanks,
> Kuba

--
Cheers,
Cheng-Yang