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

Jason Wang
2024-05-16T04:49:08Z

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.