netdev - Re: [PATCH RFC net-next 4/4] net/sched: sch_cake: share shaper state across sub-instances of cake

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Message-ID: <m2ecrusy11.fsf@gmail.com>
Date: Thu, 25 Sep 2025 10:04:58 +0100
From: Donald Hunter <donald.hunter@...il.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>
Cc: Toke Høiland-Jørgensen <toke@...e.dk>,  Jamal Hadi
 Salim
 <jhs@...atatu.com>,  Cong Wang <xiyou.wangcong@...il.com>,  Jiri Pirko
 <jiri@...nulli.us>,  "David S. Miller" <davem@...emloft.net>,  Eric
 Dumazet <edumazet@...gle.com>,  Jakub Kicinski <kuba@...nel.org>,  Paolo
 Abeni <pabeni@...hat.com>,  Simon Horman <horms@...nel.org>,  Jonas
 Köppeler <j.koeppeler@...berlin.de>,
  cake@...ts.bufferbloat.net,
  netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next 4/4] net/sched: sch_cake: share shaper
 state across sub-instances of cake_mq

Toke Høiland-Jørgensen <toke@...hat.com> writes:

> From: Jonas Köppeler <j.koeppeler@...berlin.de>
>
> This commit adds shared shaper state across the cake instances beneath a
> cake_mq qdisc. It works by periodically tracking the number of active
> instances, and scaling the configured rate by the number of active
> queues.
>
> The scan is lockless and simply reads the qlen and the last_active state
> variable of each of the instances configured beneath the parent cake_mq
> instance. Locking is not required since the values are only updated by
> the owning instance, and eventual consistency is sufficient for the
> purpose of estimating the number of active queues.
>
> The interval for scanning the number of active queues is configurable
> and defaults to 200 us. We found this to be a good tradeoff between
> overhead and response time. For a detailed analysis of this aspect see
> the Netdevconf talk:
>
> https://netdevconf.info/0x19/docs/netdev-0x19-paper16-talk-paper.pdf
>
> Signed-off-by: Jonas Köppeler <j.koeppeler@...berlin.de>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  include/uapi/linux/pkt_sched.h |  2 ++
>  net/sched/sch_cake.c           | 67 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 69 insertions(+)
>
> diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
> index c2da76e78badebbdf7d5482cef1a3132aec99fe1..a4aa812bfbe86424c502de5bb2e5b1429b440088 100644
> --- a/include/uapi/linux/pkt_sched.h
> +++ b/include/uapi/linux/pkt_sched.h
> @@ -1014,6 +1014,7 @@ enum {
>  	TCA_CAKE_ACK_FILTER,
>  	TCA_CAKE_SPLIT_GSO,
>  	TCA_CAKE_FWMARK,
> +	TCA_CAKE_SYNC_TIME,
>  	__TCA_CAKE_MAX
>  };
>  #define TCA_CAKE_MAX	(__TCA_CAKE_MAX - 1)
> @@ -1036,6 +1037,7 @@ enum {
>  	TCA_CAKE_STATS_DROP_NEXT_US,
>  	TCA_CAKE_STATS_P_DROP,
>  	TCA_CAKE_STATS_BLUE_TIMER_US,
> +	TCA_CAKE_STATS_ACTIVE_QUEUES,
>  	__TCA_CAKE_STATS_MAX
>  };
>  #define TCA_CAKE_STATS_MAX (__TCA_CAKE_STATS_MAX - 1)

Hi Toke,

Could you include this diff in the patch to keep the ynl spec up to date?

diff --git a/Documentation/netlink/specs/tc.yaml b/Documentation/netlink/specs/tc.yaml
index b398f7a46dae..f0edc84f9613 100644
--- a/Documentation/netlink/specs/tc.yaml
+++ b/Documentation/netlink/specs/tc.yaml
@@ -2153,6 +2153,9 @@ attribute-sets:
       -
         name: fwmark
         type: u32
+      -
+        name: sync-time
+        type: u32
   -
     name: cake-stats-attrs
     name-prefix: tca-cake-stats-
@@ -2207,6 +2210,9 @@ attribute-sets:
       -
         name: blue-timer-us
         type: s32
+      -
+        name: active-queues
+        type: u32
   -
     name: cake-tin-stats-attrs
     name-prefix: tca-cake-tin-stats-