netdev - Re: [PATCH net-next v3] net: dqs: introduce IFF_NO

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Message-ID: <Zmqk5ODEKYcQerWS@nanopsycho.orion>
Date: Thu, 13 Jun 2024 09:51:00 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	davem@...emloft.net, dsahern@...nel.org, mst@...hat.com,
	jasowang@...hat.com, xuanzhuo@...ux.alibaba.com,
	eperezma@...hat.com, leitao@...ian.org, netdev@...r.kernel.org,
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v3] net: dqs: introduce IFF_NO_BQL private flag
 for non-BQL drivers

Thu, Jun 13, 2024 at 09:24:27AM CEST, kerneljasonxing@...il.com wrote:
>On Thu, Jun 13, 2024 at 3:19 PM Jiri Pirko <jiri@...nulli.us> wrote:
>>
>> Thu, Jun 13, 2024 at 08:08:36AM CEST, kerneljasonxing@...il.com wrote:
>> >On Thu, Jun 13, 2024 at 1:38 PM Jiri Pirko <jiri@...nulli.us> wrote:
>> >>
>> >> Thu, Jun 13, 2024 at 04:35:49AM CEST, kerneljasonxing@...il.com wrote:
>> >> >From: Jason Xing <kernelxing@...cent.com>
>> >> >
>> >> >Since commit 74293ea1c4db6 ("net: sysfs: Do not create sysfs for non
>> >> >BQL device") limits the non-BQL driver not creating byte_queue_limits
>> >> >directory, I found there is one exception, namely, virtio-net driver,
>> >> >which should also be limited in netdev_uses_bql(). Let me give it a
>> >> >try first.
>> >> >
>> >> >I decided to introduce a NO_BQL bit because:
>> >> >1) it can help us limit virtio-net driver for now.
>> >> >2) if we found another non-BQL driver, we can take it into account.
>> >> >3) we can replace all the driver meeting those two statements in
>> >> >netdev_uses_bql() in future.
>> >> >
>> >> >For now, I would like to make the first step to use this new bit for dqs
>> >> >use instead of replacing/applying all the non-BQL drivers in one go.
>> >> >
>> >> >As Jakub said, "netdev_uses_bql() is best effort", I think, we can add
>> >> >new non-BQL drivers as soon as we find one.
>> >> >
>> >> >After this patch, there is no byte_queue_limits directory in virtio-net
>> >> >driver.
>> >>
>> >> Please note following patch is currently trying to push bql support for
>> >> virtio_net:
>> >> https://lore.kernel.org/netdev/20240612170851.1004604-1-jiri@resnulli.us/
>> >
>> >I saw this one this morning and I'm reviewing/testing it.
>> >
>> >>
>> >> When that is merged, this patch is not needed. Could we wait?
>> >
>> >Please note this patch is not only written for virtio_net driver.
>> >Virtio_net driver is one of possible cases.
>>
>> Yeah, but without virtio_net, there will be no users. What's the point
>> of having that in code? I mean, in general, no-user kernel code gets
>> removed.
>
>Are you sure netdev_uses_bql() can limit all the non-bql drivers with
>those two checks? I haven't investigated this part.

Nope. What I say is, if there are other users, let's find them and let
them use what you are introducing here. Otherwise don't add unused code.

>
>>
>>
>> >
>> >After your patch gets merged (I think it will take some time), you
>> >could simply remove that one line in virtio_net.c.
>> >
>> >Thanks.