netdev - Re: [patch net-next] virtio_net: add support for Byte Queue Limits

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Message-ID: <20240510072431-mutt-send-email-mst@kernel.org>
Date: Fri, 10 May 2024 07:27:08 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, jasowang@...hat.com,
	xuanzhuo@...ux.alibaba.com, virtualization@...ts.linux.dev,
	ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
	john.fastabend@...il.com
Subject: Re: [patch net-next] virtio_net: add support for Byte Queue Limits

On Fri, May 10, 2024 at 01:11:49PM +0200, Jiri Pirko wrote:
> Fri, May 10, 2024 at 12:52:52PM CEST, mst@...hat.com wrote:
> >On Fri, May 10, 2024 at 12:37:15PM +0200, Jiri Pirko wrote:
> >> Thu, May 09, 2024 at 04:28:12PM CEST, mst@...hat.com wrote:
> >> >On Thu, May 09, 2024 at 03:31:56PM +0200, Jiri Pirko wrote:
> >> >> Thu, May 09, 2024 at 02:41:39PM CEST, mst@...hat.com wrote:
> >> >> >On Thu, May 09, 2024 at 01:46:15PM +0200, Jiri Pirko wrote:
> >> >> >> From: Jiri Pirko <jiri@...dia.com>
> >> >> >> 
> >> >> >> Add support for Byte Queue Limits (BQL).
> >> >> >> 
> >> >> >> Signed-off-by: Jiri Pirko <jiri@...dia.com>
> >> >> >
> >> >> >Can we get more detail on the benefits you observe etc?
> >> >> >Thanks!
> >> >> 
> >> >> More info about the BQL in general is here:
> >> >> https://lwn.net/Articles/469652/
> >> >
> >> >I know about BQL in general. We discussed BQL for virtio in the past
> >> >mostly I got the feedback from net core maintainers that it likely won't
> >> >benefit virtio.
> >> 
> >> Do you have some link to that, or is it this thread:
> >> https://lore.kernel.org/netdev/21384cb5-99a6-7431-1039-b356521e1bc3@redhat.com/
> >
> >
> >A quick search on lore turned up this, for example:
> >https://lore.kernel.org/all/a11eee78-b2a1-3dbc-4821-b5f4bfaae819@gmail.com/
> 
> Says:
> "Note that NIC with many TX queues make BQL almost useless, only adding extra
>  overhead."
> 
> But virtio can have one tx queue, I guess that could be quite common
> configuration in lot of deployments.

Not sure we should worry about performance for these though.
What I am saying is this should come with some benchmarking
results.


> 
> >
> >
> >
> >
> >> I don't see why virtio should be any different from other
> >> drivers/devices that benefit from bql. HOL blocking is the same here are
> >> everywhere.
> >> 
> >> >
> >> >So I'm asking, what kind of benefit do you observe?
> >> 
> >> I don't have measurements at hand, will attach them to v2.
> >> 
> >> Thanks!
> >> 
> >> >
> >> >-- 
> >> >MST
> >> >
> >