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

Jiri Pirko
2024-05-16T15:25:27Z

Thu, May 16, 2024 at 02:31:59PM CEST, mst@redhat.com wrote:
>On Thu, May 16, 2024 at 12:54:58PM +0200, Jiri Pirko wrote:
>> 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.
>
>Seems the results became much noisier? Also

Not enough data to assume that I believe.

>I'd expect a regression if any to be in a streaming benchmark.

Can you elaborate?

>
>--
>MST
>