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From: Michael Walle <michael@walle.cc>
To: Vladimir Oltean <vladimir.oltean@nxp.com>
Cc: Xiaoliang Yang <xiaoliang.yang_1@nxp.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	UNGLinuxDriver@microchip.com, alexandre.belloni@bootlin.com,
	allan.nielsen@microchip.com,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	davem@davemloft.net, idosch@mellanox.com,
	joergen.andreasen@microchip.com, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, Po Liu <po.liu@nxp.com>,
	vinicius.gomes@intel.com
Subject: Re: [net-next] net: dsa: felix: disable always guard band bit for TAS config
Date: Mon, 07 Jun 2021 13:26:22 +0200	[thread overview]
Message-ID: <07b1bc11eee83d724d4ddc4ee8378a12@walle.cc> (raw)
In-Reply-To: <20210507121909.ojzlsiexficjjjun@skbuf>

Hi Vladimir, Hi Xiaoliang,

Am 2021-05-07 14:19, schrieb Vladimir Oltean:
> Devices like Felix need the per-queue max SDU from the
> user - if that isn's specified in the netlink message they'll have to
> default to the interface's MTU.

Btw. just to let you and Xiaoliang know:

It appears that PORT_MAX_SDU isn't working as expected. It is used
as a fallback if QMAXSDU_CFG_n isn't set for the guard band
calculation. But it appears to be _not_ used for discarding any
frames. E.g. if you set PORT_MAX_SDU to 500 the port will still
happily send frames larger than 500 bytes. (Unless of course
you hit the guard band of 500 bytes). OTOH QMAXSDU_CFG_n works
as expected, it will discard oversized frames - and presumly will
set the guard band accordingly, I haven't tested this explicitly.

Thus, I wonder what sense PORT_MAX_SDU makes at all. If you set
the guard band to a smaller value than the MTU, you'll also need
to make sure, there will be no larger frames scheduled on that port.

In any case, the workaround is to set QMAXSDU_CFG_n (for all
n=0..7) to the desired max_sdu value instead of using PORT_MAX_SDU.

It might also make sense to check with the IP supplier.

In the case anyone wants to implement that for (upstream) linux ;)

-michael

  parent reply	other threads:[~2021-06-07 11:26 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-19 10:25 [net-next] net: dsa: felix: disable always guard band bit for TAS config Xiaoliang Yang
2021-04-19 12:38 ` Vladimir Oltean
2021-04-20  3:06   ` [EXT] " Xiaoliang Yang
2021-04-20  8:26     ` Vladimir Oltean
2021-04-20 10:28       ` Xiaoliang Yang
2021-04-20 10:30         ` Vladimir Oltean
2021-04-20 10:42           ` Vladimir Oltean
2021-04-21  2:51             ` Xiaoliang Yang
2021-04-20 10:33 ` Vladimir Oltean
2021-04-20 23:20 ` patchwork-bot+netdevbpf
2021-05-04 17:05 ` Michael Walle
2021-05-04 18:18   ` Vladimir Oltean
2021-05-04 18:38     ` Michael Walle
2021-05-04 18:50       ` Vladimir Oltean
2021-05-04 19:08         ` Michael Walle
2021-05-04 19:17           ` Vladimir Oltean
2021-05-04 20:23             ` Michael Walle
2021-05-04 21:33               ` Vladimir Oltean
2021-05-06 13:25                 ` Michael Walle
2021-05-06 13:50                   ` Vladimir Oltean
2021-05-06 14:20                     ` Michael Walle
2021-05-06 14:41                     ` Michael Walle
2021-05-06 15:07                       ` Vladimir Oltean
2021-05-06 18:28                         ` Michael Walle
2021-05-07  7:16                   ` [EXT] " Xiaoliang Yang
2021-05-07  7:35                     ` Michael Walle
2021-05-07 11:09                       ` Xiaoliang Yang
2021-05-07 12:19                         ` Vladimir Oltean
2021-05-07 12:43                           ` Michael Walle
2021-06-07 11:26                           ` Michael Walle [this message]
2021-06-09  8:06                             ` [EXT] " Xiaoliang Yang
2021-06-09  8:41                               ` Michael Walle
2021-05-07 12:19                         ` Michael Walle

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