netdev - Re: [PATCH] net: stmmac: Change the busy-wait loops timing

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Message-ID: <20250607162110.GB197663@horms.kernel.org>
Date: Sat, 7 Jun 2025 17:21:10 +0100
From: Simon Horman <horms@...nel.org>
To: Bartlomiej Dziag <bartlomiejdziag@...il.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Daniel Machon <daniel.machon@...rochip.com>,
	Wojciech Drewek <wojciech.drewek@...el.com>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	Alexis Lothoré <alexis.lothore@...tlin.com>,
	netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: stmmac: Change the busy-wait loops timing

On Fri, Jun 06, 2025 at 12:19:49PM +0200, Bartlomiej Dziag wrote:
> After writing a new value to the PTP_TAR or PTP_STSUR registers,
> the driver waits for the addend/adjust operations to complete.
> Sometimes, the first check operation fails, resulting in
> a 10 milliseconds busy-loop before performing the next check.
> Since updating the registers takes much less than 10 milliseconds,
> the kernel gets stuck unnecessarily. This may increase the CPU usage.
> Fix that with changing the busy-loop interval to 5 microseconds.
> The registers will be checked more often.

Hi Bartlomiej,

I am curious.

Does it always take much less than 10ms, or is that usually so.
If it is the former, then do we need to wait for in the order of
10000 x 5us = 50ms before giving up?

> 
> Signed-off-by: Bartlomiej Dziag <bartlomiejdziag@...il.com>

...