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Message-ID: <ee37f457-3d2d-4c18-b22f-dfb315b3c078@davidv.dev>
Date: Sat, 10 Feb 2024 00:15:42 +0100
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Subject: Re: [PATCH v2 1/2] net: make driver settling time configurable
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To: Andrew Lunn <andrew@lunn.ch>, Jakub Kicinski <kuba@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>, "David S. Miller"
 <davem@davemloft.net>, David Ahern <dsahern@kernel.org>,
 Eric Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 "Paul E. McKenney" <paulmck@kernel.org>, Randy Dunlap
 <rdunlap@infradead.org>, Xiongwei Song <xiongwei.song@windriver.com>,
 "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
 open list <linux-kernel@vger.kernel.org>,
 "open list:NETWORKING [IPv4/IPv6]" <netdev@vger.kernel.org>
References: <20240208093722.246930-1-david@davidv.dev>
 <20240208095358.251381-1-david@davidv.dev>
 <20240209135944.265953be@kernel.org>
 <7485f0b2-93fe-4c82-95e8-5b0e10f9fa7a@lunn.ch>
From: David <david@davidv.dev>
In-Reply-To: <7485f0b2-93fe-4c82-95e8-5b0e10f9fa7a@lunn.ch>
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On 2/9/24 23:11, Andrew Lunn wrote:
> On Fri, Feb 09, 2024 at 01:59:44PM -0800, Jakub Kicinski wrote:
>> On Thu,  8 Feb 2024 10:52:29 +0100 David Ventura wrote:
>>> During IP auto configuration, some drivers apparently need to wait a
>>> certain length of time to settle; as this is not true for all drivers,
>>> make this length of time configurable.
>> Please CC folks who gave you feedback, Andrew's is missing.
Thanks for the feedback, still learning this workflow
>>
>> Andrew, what do you think about just removing the wait?
>> Or decreasing it to 1ms?
>> It feels a little wasteful to be adding uAPI for something
>> which as you said is likely papering over ancient bugs. We'll
>> fix the bugs which are still around and the uAPI will stay
>> forever :(
> My guess is, the broken drivers are doing setup stuff after they call
> netdev_register().
>
> Reducing it to 1ms will probably continue to hide such bugs. So we
> could just go with that, and probably not see any regressions. Or we
> can decide we really do want to know about broken drivers, and just
> remove the delay.
>
> Either way, we don't need a new uAPI.

Would it make sense to move this to a build-time configuration flag?

I do not have a gut-feeling for which behaviors should be configurable

at build vs run time.

> David, is 1ms too long for you? If we do take the delay out, you are
> going to receive some of the flack from regression reports.

I've used this patch to experiment with different values, and the sleep time

behaves as described in Documentation/timers/timers-howto.rst, that is, a

call of `msleep(1)` usually delays boot time by 12~13 ms in my tests.

On top of this, I'm running this specific example on a no-smp systemm, 
where I

do not believe the `msleep` achieves anything (but I'm a kernel newbie 
so please

correct me if I'm wrong).

>
>        Andrew
>