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From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
To: Jonas =?utf-8?Q?K=C3=B6ppeler?= <j.koeppeler@tu-berlin.de>, Jamal Hadi
 Salim
 <jhs@mojatatu.com>, Jiri Pirko <jiri@resnulli.us>, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Jakub Kicinski
 <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>, Simon Horman
 <horms@kernel.org>
Cc: cake@lists.bufferbloat.net, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org, Jonas =?utf-8?Q?K=C3=B6ppeler?=
 <j.koeppeler@tu-berlin.de>,
 Mike Pham <mikepham4321@gmail.com>
Subject: Re: [PATCH net-next] net/sched: sch_cake: skip clearing unused tins
 during rate adjustment
In-Reply-To: <20260716-sch_cake-skip-clearing-tins-v1-1-d9787df20c28@tu-berlin.de>
References: <20260716-sch_cake-skip-clearing-tins-v1-1-d9787df20c28@tu-berlin.de>
Date: Fri, 17 Jul 2026 10:31:37 +0200
X-Clacks-Overhead: GNU Terry Pratchett
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Jonas K=C3=B6ppeler <j.koeppeler@tu-berlin.de> writes:

> When cake_configure_rates() is called from the dequeue path with
> rate_adjust=3Dtrue, 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 K=C3=B6ppeler <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