netdev - Re: [Intel-wired-lan] [PATCH iwl-net v2 1/1] igc: Fix packet still tx after gate close by reducing i226 MAC retry buffer

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Message-ID: <3fa847cd-67f3-470c-b375-993aabc6decb@intel.com>
Date: Thu, 1 Aug 2024 10:26:27 +0300
From: Mor Bar-Gabay <morx.bar.gabay@...el.com>
To: Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>, "David S . Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Jesse Brandeburg
	<jesse.brandeburg@...el.com>, Tony Nguyen <anthony.l.nguyen@...el.com>,
	Vinicius Costa Gomes <vinicius.gomes@...el.com>, Paul Menzel
	<pmenzel@...gen.mpg.de>
CC: <netdev@...r.kernel.org>, <intel-wired-lan@...ts.osuosl.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [PATCH iwl-net v2 1/1] igc: Fix packet still tx
 after gate close by reducing i226 MAC retry buffer

On 06/07/2024 18:38, Faizal Rahim wrote:
> Testing uncovered that even when the taprio gate is closed, some packets
> still transmit.
> 
> According to i225/6 hardware errata [1], traffic might overflow the
> planned QBV window. This happens because MAC maintains an internal buffer,
> primarily for supporting half duplex retries. Therefore, even when the
> gate closes, residual MAC data in the buffer may still transmit.
> 
> To mitigate this for i226, reduce the MAC's internal buffer from 192 bytes
> to the recommended 88 bytes by modifying the RETX_CTL register value.
> 
> This follows guidelines from:
> [1] Ethernet Controller I225/I22 Spec Update Rev 2.1 Errata Item 9:
>      TSN: Packet Transmission Might Cross Qbv Window
> [2] I225/6 SW User Manual Rev 1.2.4: Section 8.11.5 Retry Buffer Control
> 
> Note that the RETX_CTL register can't be used in TSN mode because half
> duplex feature cannot coexist with TSN.
> 
> Test Steps:
> 1.  Send taprio cmd to board A:
>      tc qdisc replace dev enp1s0 parent root handle 100 taprio \
>      num_tc 4 \
>      map 3 2 1 0 3 3 3 3 3 3 3 3 3 3 3 3 \
>      queues 1@0 1@1 1@2 1@3 \
>      base-time 0 \
>      sched-entry S 0x07 500000 \
>      sched-entry S 0x0f 500000 \
>      flags 0x2 \
>      txtime-delay 0
> 
>      Note that for TC3, gate should open for 500us and close for another
>      500us.
> 
> 3.  Take tcpdump log on Board B.
> 
> 4.  Send udp packets via UDP tai app from Board A to Board B.
> 
> 5.  Analyze tcpdump log via wireshark log on Board B. Ensure that the
>      total time from the first to the last packet received during one cycle
>      for TC3 does not exceed 500us.
> 
> Signed-off-by: Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>
> Acked-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> ---
> v1: https://patchwork.kernel.org/project/netdevbpf/patch/20240701100058.3301229-1-faizal.abdul.rahim@linux.intel.com/
> 
> Changelog:
> v1 -> v2
> - Update commit description (Paul).
> - Rename qbvfullth -> qbvfullthreshold (Paul).
> ---
>   drivers/net/ethernet/intel/igc/igc_defines.h |  6 ++++
>   drivers/net/ethernet/intel/igc/igc_tsn.c     | 34 ++++++++++++++++++++
>   2 files changed, 40 insertions(+)
> 
Tested-by: Mor Bar-Gabay <morx.bar.gabay@...el.com>