[Cake] [PATCH net-next] net/sched: cake: avoid separate allocation of struct cake_sched_config

[Cake] [PATCH net-next] net/sched: cake: avoid separate allocation of struct cake_sched_config

[Toke Høiland-Jørgensen]

Paolo pointed out that we can avoid separately allocating struct
cake_sched_config even in the non-mq case, by embedding it into struct
cake_sched_data. This reduces the complexity of the logic that swaps the
pointers and frees the old value, at the cost of adding 56 bytes to the
latter. Since cake_sched_data is already almost 17k bytes, this seems
like a reasonable tradeoff.

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 net/sched/sch_cake.c | 29 ++++++-----------------------
 1 file changed, 6 insertions(+), 23 deletions(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index e30ef7f8ee68..fd56b7d88301 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -221,6 +221,7 @@ struct cake_sched_data {
 	struct tcf_block *block;
 	struct cake_tin_data *tins;
 	struct cake_sched_config *config;
+	struct cake_sched_config initial_config;
 
 	struct cake_heap_entry overflow_heap[CAKE_QUEUES * CAKE_MAX_TINS];
 
@@ -2798,8 +2799,6 @@ static void cake_destroy(struct Qdisc *sch)
 	qdisc_watchdog_cancel(&q->watchdog);
 	tcf_block_put(q->block);
 	kvfree(q->tins);
-	if (q->config && !q->config->is_shared)
-		kvfree(q->config);
 }
 
 static void cake_config_init(struct cake_sched_config *q, bool is_shared)
@@ -2822,13 +2821,9 @@ static int cake_init(struct Qdisc *sch, struct nlattr *opt,
 		     struct netlink_ext_ack *extack)
 {
 	struct cake_sched_data *qd = qdisc_priv(sch);
-	struct cake_sched_config *q;
+	struct cake_sched_config *q = &qd->initial_config;
 	int i, j, err;
 
-	q = kzalloc(sizeof(*q), GFP_KERNEL);
-	if (!q)
-		return -ENOMEM;
-
 	cake_config_init(q, false);
 
 	sch->limit = 10240;
@@ -2842,14 +2837,13 @@ static int cake_init(struct Qdisc *sch, struct nlattr *opt,
 
 	if (opt) {
 		err = cake_change(sch, opt, extack);
-
 		if (err)
-			goto err;
+			return err;
 	}
 
 	err = tcf_block_get(&qd->block, &qd->filter_list, sch, extack);
 	if (err)
-		goto err;
+		return err;
 
 	quantum_div[0] = ~0;
 	for (i = 1; i <= CAKE_QUEUES; i++)
@@ -2857,10 +2851,8 @@ static int cake_init(struct Qdisc *sch, struct nlattr *opt,
 
 	qd->tins = kvcalloc(CAKE_MAX_TINS, sizeof(struct cake_tin_data),
 			    GFP_KERNEL);
-	if (!qd->tins) {
-		err = -ENOMEM;
-		goto err;
-	}
+	if (!qd->tins)
+		return -ENOMEM;
 
 	for (i = 0; i < CAKE_MAX_TINS; i++) {
 		struct cake_tin_data *b = qd->tins + i;
@@ -2893,22 +2885,13 @@ static int cake_init(struct Qdisc *sch, struct nlattr *opt,
 	qd->last_checked_active = 0;
 
 	return 0;
-err:
-	kvfree(qd->config);
-	qd->config = NULL;
-	return err;
 }
 
 static void cake_config_replace(struct Qdisc *sch, struct cake_sched_config *cfg)
 {
 	struct cake_sched_data *qd = qdisc_priv(sch);
-	struct cake_sched_config *q = qd->config;
 
 	qd->config = cfg;
-
-	if (!q->is_shared)
-		kvfree(q);
-
 	cake_reconfigure(sch);
 }
 
-- 
2.52.0

[Cake] Re: [PATCH net-next] net/sched: cake: avoid separate allocation of struct cake_sched_config

[Eric Dumazet]

On Tue, Jan 13, 2026 at 3:32 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Paolo pointed out that we can avoid separately allocating struct
> cake_sched_config even in the non-mq case, by embedding it into struct
> cake_sched_data. This reduces the complexity of the logic that swaps the
> pointers and frees the old value, at the cost of adding 56 bytes to the
> latter. Since cake_sched_data is already almost 17k bytes, this seems
> like a reasonable tradeoff.
>
> Suggested-by: Paolo Abeni <pabeni@redhat.com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---

This is also fixing a panic, so :

Fixes: bc0ce2bad36c ("net/sched: sch_cake: Factor out config variables
into separate struct")

For the record, a fix for the panic would be :

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index e30ef7f8ee6862a916acc06e568e37f35fd675b1..742fb850e2afb159f215b263bc36c372552911bc
100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -2825,6 +2825,8 @@ static int cake_init(struct Qdisc *sch, struct
nlattr *opt,
        struct cake_sched_config *q;
        int i, j, err;

+       qdisc_watchdog_init(&qd->watchdog, sch);
+
        q = kzalloc(sizeof(*q), GFP_KERNEL);
        if (!q)
                return -ENOMEM;
@@ -2838,7 +2840,6 @@ static int cake_init(struct Qdisc *sch, struct
nlattr *opt,
        qd->cur_flow  = 0;
        qd->config = q;

-       qdisc_watchdog_init(&qd->watchdog, sch);

        if (opt) {
                err = cake_change(sch, opt, extack);

[Cake] Re: [PATCH net-next] net/sched: cake: avoid separate allocation of struct cake_sched_config

[Toke Høiland-Jørgensen]

Eric Dumazet <edumazet@google.com> writes:

> On Tue, Jan 13, 2026 at 3:32 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>>
>> Paolo pointed out that we can avoid separately allocating struct
>> cake_sched_config even in the non-mq case, by embedding it into struct
>> cake_sched_data. This reduces the complexity of the logic that swaps the
>> pointers and frees the old value, at the cost of adding 56 bytes to the
>> latter. Since cake_sched_data is already almost 17k bytes, this seems
>> like a reasonable tradeoff.
>>
>> Suggested-by: Paolo Abeni <pabeni@redhat.com>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> ---
>
> This is also fixing a panic, so :
>
> Fixes: bc0ce2bad36c ("net/sched: sch_cake: Factor out config variables
> into separate struct")
>
> For the record, a fix for the panic would be :

Ah yes, of course; thanks for noticing (and for the tag)!

-Toke

[Cake] Re: [PATCH net-next] net/sched: cake: avoid separate allocation of struct cake_sched_config

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 13 Jan 2026 15:31:56 +0100 you wrote:
> Paolo pointed out that we can avoid separately allocating struct
> cake_sched_config even in the non-mq case, by embedding it into struct
> cake_sched_data. This reduces the complexity of the logic that swaps the
> pointers and frees the old value, at the cost of adding 56 bytes to the
> latter. Since cake_sched_data is already almost 17k bytes, this seems
> like a reasonable tradeoff.
> 
> [...]

Here is the summary with links:
  - [net-next] net/sched: cake: avoid separate allocation of struct cake_sched_config
    https://git.kernel.org/netdev/net-next/c/2a85541d95f7

You are awesome, thank you!
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