netdev - Re: [PATCH net] net: stmmac: dwmac-imx: request high frequency mode

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Date: Wed, 4 Oct 2023 14:59:51 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Shenwei Wang <shenwei.wang@....com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Shawn Guo
 <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, Maxime
 Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>,
 Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam
 <festevam@...il.com>, NXP Linux Team <linux-imx@....com>,
 netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-stm32@...md-mailman.stormreply.com, imx@...ts.linux.dev, Mario
 Castaneda <mario.ignacio.castaneda.lopez@....com>
Subject: Re: [PATCH net] net: stmmac: dwmac-imx: request high frequency mode

On Wed,  4 Oct 2023 14:54:42 -0500 Shenwei Wang wrote:
> Some i.MX SoCs like the i.mx8mq support adjusting the frequency of the
> DDR, AHB, and AXI buses based on system loading. If the dwmac interface
> in the driver does not request a HIGH frequency, it can significantly
> degrade performance when the system switches to a lower frequency to
> conserve power.
> 
> For example, on an i.MX8MQ EVK board, the throughput dropped to around
> 100Mbit/s on a 1Gbit connection:
> 
>     [ ID] Interval           Transfer     Bitrate
>     [  5]   0.00-10.00  sec   117 MBytes  97.9 Mbits/sec
> 
> However, throughput can return to expected levels after its driver requests
> the high frequency mode. Requesting high frequency in the dwmac driver is
> essential to maintain full throughput when the i.MX SoC adjusts bus speeds
> for power savings.

Oh, another one in one day :S Although this one feels much more like
a bug that escaped testing because testing didn't use power saving?
In any case, do you happen to have a user report you can mention here?
Quoting stable rules:

| Serious issues as reported by a user of a distribution kernel may also
| be considered if they fix a notable performance or interactivity
| issue. As these fixes are not as obvious and have a higher risk of a
| subtle regression they should only be submitted by a distribution
| kernel maintainer and include an addendum linking to a bugzilla entry
| if it exists and additional information on the user-visible impact.

And a Fixes tag would be good, please add.
-- 
pw-bot: cr