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Date: Mon, 19 Feb 2024 10:46:31 +0000
From: Simon Horman <horms@kernel.org>
To: Eric Dumazet <edumazet@google.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
	Stephen Hemminger <stephen@networkplumber.org>,
	Breno Leitao <leitao@debian.org>, kuba@kernel.org,
	davem@davemloft.net, pabeni@redhat.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Johannes Berg <johannes.berg@intel.com>
Subject: Re: [PATCH net-next v2] net: sysfs: Do not create sysfs for non BQL
 device
Message-ID: <20240219104631.GX40273@kernel.org>
References: <20240216094154.3263843-1-leitao@debian.org>
 <20240216092905.4e2d3c7c@hermes.local>
 <0e0ba573-1ae0-4a4b-8286-fdbc8dbe7639@gmail.com>
 <CANn89i+5F7d4i7Ds4V6TtkzzAjQjNQ8xOeoYqZr8tY6tWWmMEg@mail.gmail.com>
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On Fri, Feb 16, 2024 at 07:45:37PM +0100, Eric Dumazet wrote:
> On Fri, Feb 16, 2024 at 7:41 PM Florian Fainelli <f.fainelli@gmail.com> wrote:
> >
> > On 2/16/24 09:29, Stephen Hemminger wrote:
> > > On Fri, 16 Feb 2024 01:41:52 -0800
> > > Breno Leitao <leitao@debian.org> wrote:
> > >
> > >> +static bool netdev_uses_bql(const struct net_device *dev)
> > >> +{
> > >> +    if (dev->features & NETIF_F_LLTX ||
> > >> +        dev->priv_flags & IFF_NO_QUEUE)
> > >> +            return false;
> > >> +
> > >> +    return IS_ENABLED(CONFIG_BQL);
> > >> +}
> > >
> > > Various compilers will warn about missing parens in that expression.
> > > It is valid but mixing & and || can be bug trap.
> > >
> > >       if ((dev->features & NETIF_F_LLTX) || (dev->priv_flags & IFF_NO_QUEUE))
> > >               return false;
> > >
> > > Not all drivers will be using bql, it requires driver to have that code.
> > > So really it means driver could be using BQL.
> > > Not sure if there is a way to find out if driver has the required BQL bits.
> >
> > There is not a feature flag to be keying off if that is what you are
> > after, you would need to audit the drivers and see whether they make
> > calls to netdev_tx_sent_queue(), netdev_tx_reset_queue(),
> > netdev_tx_completed_queue().
> >
> > I suppose you might be able to programmatically extract that information
> > by looking at whether a given driver object file has a reference to
> > dql_{reset,avail,completed} or do that at the source level, whichever is
> > easier.
> 
> Note that the suggested patch does not change current functionality.
> 
> Traditionally, we had sysfs entries fpr BQL for all netdev, regardless of them
> using BQL or not.
> 
> The patch seems to be a good first step.
> 
> If anyone wants to refine it further, this is great, but I suspect
> very few users will benefit from
> having less sysfs entries for real/physical devices....
> 

From my point of view the main advantage in not having these entries
would be that it is really a bit confusing for them to be there
that don't use BQL. But I agree, that is (also) likely to benefit
few users.

In any case, I agree this is a good first step.