linux-kernel - Re: [PATCH net] net: napi: Make napi_defer

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Message-ID: <CANn89iLhrKyFKf9DpJSSM9CZ9sgoRo7jovg2GhjsJABoqzzVsQ@mail.gmail.com>
Date: Mon, 2 Sep 2024 19:00:48 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Joe Damato <jdamato@...tly.com>, Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org, 
	mkarsten@...terloo.ca, stable@...nel.org, Jakub Kicinski <kuba@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, 
	Jonathan Corbet <corbet@....net>, Breno Leitao <leitao@...ian.org>, 
	Johannes Berg <johannes.berg@...el.com>, Heiner Kallweit <hkallweit1@...il.com>, 
	Alexander Lobakin <aleksander.lobakin@...el.com>, 
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: napi: Make napi_defer_irqs u32

On Mon, Sep 2, 2024 at 6:29 PM Joe Damato <jdamato@...tly.com> wrote:
>
> On Mon, Sep 02, 2024 at 03:01:28PM +0200, Eric Dumazet wrote:
> > On Sat, Aug 31, 2024 at 1:32 PM Joe Damato <jdamato@...tly.com> wrote:
> > >
> > > In commit 6f8b12d661d0 ("net: napi: add hard irqs deferral feature")
> > > napi_defer_irqs was added to net_device and napi_defer_irqs_count was
> > > added to napi_struct, both as type int.
> > >
> > > This value never goes below zero. Change the type for both from int to
> > > u32, and add an overflow check to sysfs to limit the value to S32_MAX.
> > >
> > > Before this patch:
> > >
> > > $ sudo bash -c 'echo 2147483649 > /sys/class/net/eth4/napi_defer_hard_irqs'
> > > $ cat /sys/class/net/eth4/napi_defer_hard_irqs
> > > -2147483647
> > >
> > > After this patch:
> > >
> > > $ sudo bash -c 'echo 2147483649 > /sys/class/net/eth4/napi_defer_hard_irqs'
> > > bash: line 0: echo: write error: Numerical result out of range
> > >
> > > Fixes: 6f8b12d661d0 ("net: napi: add hard irqs deferral feature")
> > > Cc: stable@...nel.org
> > > Cc: Eric Dumazet <edumazet@...gle.com>
> > > Suggested-by: Jakub Kicinski <kuba@...nel.org>
> > > Signed-off-by: Joe Damato <jdamato@...tly.com>
> > > ---
> >
> > I do not think this deserves a change to stable trees.
>
> OK, I can send any other revisions to -next, instead.
>
> > Signed or unsigned, what is the issue ?
> >
> > Do you really need one extra bit ?
>
> I made the maximum S32_MAX because the practical limit has always
> been S32_MAX. Any larger values overflow. Keeping it at S32_MAX does
> not change anything about existing behavior, which was my goal.
>
> Would you prefer if it was U32_MAX instead?
>
> Or are you asking me to leave it the way it is?

I think this would target net-next at most, please lets avoid hassles
for stable teams.