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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Thu, 13 Jun 2024 22:48:17 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	davem@...emloft.net, dsahern@...nel.org, 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

On Thu, Jun 13, 2024 at 10:34 PM Jiri Pirko <jiri@...nulli.us> wrote:
>
> Thu, Jun 13, 2024 at 04:11:12PM CEST, kerneljasonxing@...il.com wrote:
> >On Thu, Jun 13, 2024 at 9:17 PM Jiri Pirko <jiri@...nulli.us> wrote:
> >>
> >> Thu, Jun 13, 2024 at 11:26:05AM CEST, kerneljasonxing@...il.com wrote:
> >> >On Thu, Jun 13, 2024 at 3:56 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> >> >>
> >> >> On Thu, Jun 13, 2024 at 09:51:00AM +0200, Jiri Pirko wrote:
> >> >> > 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.
> >> >>
> >> >>
> >> >> Additionally, it looks like virtio is going to become a
> >> >> "sometimes BQL sometimes no-BQL" driver, so what's the plan -
> >> >> to set/clear the flag accordingly then? What kind of locking
> >> >> will be needed?
> >> >
> >> >Could we consider the default mode is BQL, so we can remove that new
> >> >IFF_NO_BQL flag? If it's hard to take care of these two situations, I
> >> >think we could follow this suggestion from Jakub: "netdev_uses_bql()
> >> >is best effort". What do you think?
> >>
> >> Make sense.
> >>
> >> Also, note that virtio_net bql utilization is going to be not only
> >> dynamically configured, but also per-queue. It would be hard to expose
> >> that over one device flag :)
> >
> >At that time, I would let virtio_net driver go, that is to say, I
> >wouldn't take it into consideration in netdev_uses_bql() since it's
> >too complicated.
> >
> >BTW, hope to see your per-queue configured feature patchset soon :)
>
> It's done already. See virtnet_set_per_queue_coalesce()
> if ec->tx_max_coalesced_frames is 0, napi_weight is set to 0 and napi
> orphan mode is used.

Oh right, I missed that... Thanks for reminding me.