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

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Message-ID: <Zj4A9XY7z-TzEpdz@nanopsycho.orion>
Date: Fri, 10 May 2024 13:11:49 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: "Michael S. Tsirkin" <mst@...hat.com>
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

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.


>
>
>
>
>> 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
>> >
>