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From: Eric Dumazet <edumazet@google.com>
Date: Fri, 16 Feb 2024 19:45:37 +0100
Message-ID: <CANn89i+5F7d4i7Ds4V6TtkzzAjQjNQ8xOeoYqZr8tY6tWWmMEg@mail.gmail.com>
Subject: Re: [PATCH net-next v2] net: sysfs: Do not create sysfs for non BQL device
To: Florian Fainelli <f.fainelli@gmail.com>
Cc: 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, horms@kernel.org, 
	Johannes Berg <johannes.berg@intel.com>
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On Fri, Feb 16, 2024 at 7:41=E2=80=AFPM 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_Q=
UEUE))
> >               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 b=
its.
>
> 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 t=
hem
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....