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

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Date: Wed, 15 May 2024 09:34:08 +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 01:27:08PM CEST, mst@...hat.com wrote:
>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 did some measurements with VDPA, backed by ConnectX6dx NIC, single
queue pair:

super_netperf 200 -H $ip -l 45 -t TCP_STREAM &
nice -n 20 netperf -H $ip -l 10 -t TCP_RR

RR result with no bql:
29.95
32.74
28.77

RR result with bql:
222.98
159.81
197.88



>
>
>> 
>> >
>> >
>> >
>> >
>> >> 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
>> >> >
>> >
>