diff mbox series

[net-next,2/3] net/sched: taprio: don't allow dynamic max_sdu to go negative after stab adjustment

Message ID 20230215224632.2532685-3-vladimir.oltean@nxp.com
State New
Headers
Series taprio queueMaxSDU fixes |

Commit Message

Vladimir Oltean Feb. 15, 2023, 10:46 p.m. UTC 
  The overhead specified in the size table comes from the user. With small
time intervals (or gates always closed), the overhead can be larger than
the max interval for that traffic class, and their difference is
negative.

What we want to happen is for max_sdu_dynamic to have the smallest
non-zero value possible (1) which means that all packets on that traffic
class are dropped on enqueue. However, since max_sdu_dynamic is u32, a
negative is represented as a large value and oversized dropping never
happens.

Use max_t with int to force a truncation of max_frm_len to no smaller
than dev->hard_header_len + 1, which in turn makes max_sdu_dynamic no
smaller than 1.

Fixes: fed87cc6718a ("net/sched: taprio: automatically calculate queueMaxSDU based on TC gate durations")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 net/sched/sch_taprio.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Comments

Kurt Kanzenbach Feb. 16, 2023, 9:27 a.m. UTC | #1 
On Thu Feb 16 2023, Vladimir Oltean wrote:
> The overhead specified in the size table comes from the user. With small
> time intervals (or gates always closed), the overhead can be larger than
> the max interval for that traffic class, and their difference is
> negative.
>
> What we want to happen is for max_sdu_dynamic to have the smallest
> non-zero value possible (1) which means that all packets on that traffic
> class are dropped on enqueue. However, since max_sdu_dynamic is u32, a
> negative is represented as a large value and oversized dropping never
> happens.
>
> Use max_t with int to force a truncation of max_frm_len to no smaller
> than dev->hard_header_len + 1, which in turn makes max_sdu_dynamic no
> smaller than 1.
>
> Fixes: fed87cc6718a ("net/sched: taprio: automatically calculate queueMaxSDU based on TC gate durations")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
diff mbox series

Patch

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 556e72ec0f38..53ba4d6b0218 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -279,8 +279,14 @@  static void taprio_update_queue_max_sdu(struct taprio_sched *q,
 			u32 max_frm_len;
 
 			max_frm_len = duration_to_length(q, sched->max_open_gate_duration[tc]);
-			if (stab)
+			/* Compensate for L1 overhead from size table,
+			 * but don't let the frame size go negative
+			 */
+			if (stab) {
 				max_frm_len -= stab->szopts.overhead;
+				max_frm_len = max_t(int, max_frm_len,
+						    dev->hard_header_len + 1);
+			}
 			max_sdu_dynamic = max_frm_len - dev->hard_header_len;
 		}