netdev - Re: [PATCH net v2 0/3] net: prevent deadlocks and mis-configuration with per-NAPI threaded config

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Message-ID: <20250811085258.4b6cfa79@kernel.org>
Date: Mon, 11 Aug 2025 08:52:58 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Joe Damato <joe@...a.to>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, andrew+netdev@...n.ch, horms@...nel.org,
 willemdebruijn.kernel@...il.com, skhawaja@...gle.com, sdf@...ichev.me,
 shuah@...nel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net v2 0/3] net: prevent deadlocks and mis-configuration
 with per-NAPI threaded config

On Sat, 9 Aug 2025 18:59:27 -0700 Joe Damato wrote:
> On Fri, Aug 08, 2025 at 05:12:02PM -0700, Jakub Kicinski wrote:
> > Running the test added with a recent fix on a driver with persistent
> > NAPI config leads to a deadlock. The deadlock is fixed by patch 3,
> > patch 2 is I think a more fundamental problem with the way we
> > implemented the config.
> > 
> > I hope the fix makes sense, my own thinking is definitely colored
> > by my preference (IOW how the per-queue config RFC was implemented).  
> 
> Maybe it's too late now, but I am open to revisiting how the whole per-queue
> NAPI config works after a conversation we had a couple months ago (IIRC ?).
> 
> I think you had proposed something that made sense to me at the time (although
> I can't recall what that was or what thread that was in).

FWIW the discussion was whether setting things at the device level
should override all the per-NAPI settings, or should we treat the
device level as lower priority and only apply it if user didn't set
per-NAPI override.

I guess it doesn't make a huge difference, other than that resetting 
the unused NAPIs to "unset" would remove the need for patch 2.