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

Jiri Pirko
2024-05-16T10:55:05Z

Thu, May 16, 2024 at 06:48:38AM CEST, jasowang@redhat.com wrote:
>On Wed, May 15, 2024 at 8:54 PM Jiri Pirko <jiri@resnulli.us> wrote:
>>
>> Wed, May 15, 2024 at 12:12:51PM CEST, jiri@resnulli.us wrote:
>> >Wed, May 15, 2024 at 10:20:04AM CEST, mst@redhat.com wrote:
>> >>On Wed, May 15, 2024 at 09:34:08AM +0200, Jiri Pirko wrote:
>> >>> Fri, May 10, 2024 at 01:27:08PM CEST, mst@redhat.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@redhat.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@redhat.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@redhat.com wrote:
>> >>> >> >> >> >On Thu, May 09, 2024 at 01:46:15PM +0200, Jiri Pirko wrote:
>> >>> >> >> >> >> From: Jiri Pirko <jiri@nvidia.com>
>> >>> >> >> >> >>
>> >>> >> >> >> >> Add support for Byte Queue Limits (BQL).
>> >>> >> >> >> >>
>> >>> >> >> >> >> Signed-off-by: Jiri Pirko <jiri@nvidia.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
>> >>>
>> >>
>> >>Okay. And on the other hand, any measureable degradation with
>> >>multiqueue and when testing throughput?
>> >
>> >With multiqueue it depends if the flows hits the same queue or not. If
>> >they do, the same results will likely be shown.
>>
>> RR 1q, w/o bql:
>> 29.95
>> 32.74
>> 28.77
>>
>> RR 1q, with bql:
>> 222.98
>> 159.81
>> 197.88
>>
>> RR 4q, w/o bql:
>> 355.82
>> 364.58
>> 233.47
>>
>> RR 4q, with bql:
>> 371.19
>> 255.93
>> 337.77
>>
>> So answer to your question is: "no measurable degradation with 4
>> queues".
>
>Thanks but I think we also need benchmarks in cases other than vDPA.
>For example, a simple virtualization setup.

For virtualization setup, I get this:

VIRT RR 1q, w/0 bql:
49.18
49.75
50.07

VIRT RR 1q, with bql:
51.33
47.88
40.40

No measurable/significant difference.

>