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Message-ID: <0e0ba573-1ae0-4a4b-8286-fdbc8dbe7639@gmail.com>
Date: Fri, 16 Feb 2024 10:41:52 -0800
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Subject: Re: [PATCH net-next v2] net: sysfs: Do not create sysfs for non BQL
 device
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To: Stephen Hemminger <stephen@networkplumber.org>,
 Breno Leitao <leitao@debian.org>
Cc: kuba@kernel.org, davem@davemloft.net, pabeni@redhat.com,
 edumazet@google.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
 horms@kernel.org, Johannes Berg <johannes.berg@intel.com>
References: <20240216094154.3263843-1-leitao@debian.org>
 <20240216092905.4e2d3c7c@hermes.local>
From: Florian Fainelli <f.fainelli@gmail.com>
In-Reply-To: <20240216092905.4e2d3c7c@hermes.local>
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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.
-- 
Florian