linux-kernel - Re: [PATCH net-next v3] net: dqs: add NIC stall detector based on BQL

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Date: Tue, 13 Feb 2024 10:04:57 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Breno Leitao <leitao@...ian.org>, davem@...emloft.net,
 pabeni@...hat.com, Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>, weiwan@...gle.com,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, horms@...nel.org,
 Jonathan Corbet <corbet@....net>, Randy Dunlap <rdunlap@...radead.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Johannes Berg
 <johannes.berg@...el.com>, Thomas Weißschuh
 <linux@...ssschuh.net>, "open list:TRACING"
 <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v3] net: dqs: add NIC stall detector based on
 BQL

On Tue, 13 Feb 2024 14:57:49 +0100 Eric Dumazet wrote:
> Please note that adding other sysfs entries is expensive for workloads
> creating/deleting netdev and netns often.
> 
> I _think_ we should find a way for not creating
> /sys/class/net/<interface>/queues/tx-{Q}/byte_queue_limits  directory
> and files
> for non BQL enabled devices (like loopback !)

We should try, see if anyone screams. We could use IFF_NO_QUEUE, and
NETIF_F_LLTX as a proxy for "device doesn't have a real queue so BQL 
would be pointless"? Obviously better to annotate the drivers which
do have BQL support, but there's >50 of them on a quick count..