[PATCH net-next] net/sched: sch_cake: skip clearing unused tins during rate adjustment

[PATCH net-next] net/sched: sch_cake: skip clearing unused tins during rate adjustment

[Jonas Köppeler]

When cake_configure_rates() is called from the dequeue path with
rate_adjust=true, it only needs to update the rate parameters. The
loop that clears the unused tins is both unnecessary and harmful in
this path:

 - cake_clear_tin() overwrites q->cur_tin and q->cur_flow, which are
   actively used by cake_dequeue(), corrupting the dequeue state.
 - iterating over the unused tins and their internal queues to purge
   packets adds needless overhead to the hot path.

Skip the entire loop when rate_adjust is set, as neither
cake_clear_tin() nor the mtu_time update are needed when only the
rate changes.

Fixes: 15c2715a5264 ("net/sched: sch_cake: fixup cake_mq rate adjustment for diffserv config")
Signed-off-by: Jonas Köppeler <j.koeppeler@tu-berlin.de>
Tested-by: Mike Pham <mikepham4321@gmail.com>
---
 net/sched/sch_cake.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index f78f8e950776..845e1c017714 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -2609,9 +2609,11 @@ static void cake_configure_rates(struct Qdisc *sch, u64 rate, bool rate_adjust)
 		break;
 	}
 
-	for (c = qd->tin_cnt; c < CAKE_MAX_TINS; c++) {
-		cake_clear_tin(sch, c);
-		qd->tins[c].cparams.mtu_time = qd->tins[ft].cparams.mtu_time;
+	if (!rate_adjust) {
+		for (c = qd->tin_cnt; c < CAKE_MAX_TINS; c++) {
+			cake_clear_tin(sch, c);
+			qd->tins[c].cparams.mtu_time = qd->tins[ft].cparams.mtu_time;
+		}
 	}
 
 	qd->rate_ns   = qd->tins[ft].tin_rate_ns;

---
base-commit: f6f3b36c15ed44de1fbb44e645e4fae8c4a4453e
change-id: 20260716-sch_cake-skip-clearing-tins-856812586cde

Best regards,
--  
Jonas Köppeler <j.koeppeler@tu-berlin.de>

Re: [PATCH net-next] net/sched: sch_cake: skip clearing unused tins during rate adjustment

[Toke Høiland-Jørgensen]

Jonas Köppeler <j.koeppeler@tu-berlin.de> writes:

> When cake_configure_rates() is called from the dequeue path with
> rate_adjust=true, it only needs to update the rate parameters. The
> loop that clears the unused tins is both unnecessary and harmful in
> this path:
>
>  - cake_clear_tin() overwrites q->cur_tin and q->cur_flow, which are
>    actively used by cake_dequeue(), corrupting the dequeue state.
>  - iterating over the unused tins and their internal queues to purge
>    packets adds needless overhead to the hot path.
>
> Skip the entire loop when rate_adjust is set, as neither
> cake_clear_tin() nor the mtu_time update are needed when only the
> rate changes.
>
> Fixes: 15c2715a5264 ("net/sched: sch_cake: fixup cake_mq rate adjustment for diffserv config")
> Signed-off-by: Jonas Köppeler <j.koeppeler@tu-berlin.de>
> Tested-by: Mike Pham <mikepham4321@gmail.com>

Do you have any performance numbers to show the impact of this?

-Toke