Subject: Re: [xdp-hints] [PATCH bpf-next 0/9] xsk: TX metadata

From: Stanislav Fomichev <[email-masked]>
Date: Thu, 10 Aug 2023 11:23:36 -0700

On 08/09, Jesper Dangaard Brouer wrote:
> 
> 
> On 09/08/2023 18.54, Stanislav Fomichev wrote:
> > This series implements initial TX metadata (offloads) for AF_XDP.
> > See patch #2 for the main implementation and mlx5-one for the
> > example on how to consume the metadata on the device side.
> > 
> > Starting with two types of offloads:
> > - request TX timestamp (and write it back into the metadata area)
> > - request TX checksum offload
> > 
> > Changes since last RFC:
> > - add /* private: */ comments to headers (Simon)
> > - handle metadata only in the first frag (Simon)
> > - rename xdp_hw_metadata flags (Willem)
> > - s/tmo_request_checksum/tmo_request_timestamp/ in xdp_metadata_ops
> >    comment (Willem)
> > - Documentation/networking/xsk-tx-metadata.rst
> > 
> > RFC v4: https://lore.kernel.org/bpf/[email-masked]/
> > 
> > Performance:
> > 
> > I've implemented a small xskgen tool to try to saturate single tx queue:
> > https://github.com/fomichev/xskgen/tree/master
> > 
> > Here are the performance numbers with some analysis.
> > 
> 
> What is the clock freq GHz for the CPU used for this benchmark?

That's an AMD:

model name      : AMD EPYC 7B12 64-Core Processor
cpu MHz         : 2250.071
cache size      : 512 KB

> > 1. Baseline. Running with commit eb62e6aef940 ("Merge branch 'bpf:
> > Support bpf_get_func_ip helper in uprobes'"), nothing from this series:
> > 
> > - with 1400 bytes of payload: 98 gbps, 8 mpps
> > ./xskgen -s 1400 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 116960000000 bits, took 1.189130 sec, 98.357623 gbps 8.409509 mpps
> > 
> > - with 200 bytes of payload: 49 gbps, 23 mpps
> > ./xskgen -s 200 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000064 packets 20960134144 bits, took 0.422235 sec, 49.640921 gbps 23.683645 mpps
> > 
> > 2. Adding single commit that supports reserving XDP_TX_METADATA_LEN
> >     changes nothing numbers-wise.
> > 
> > - baseline for 1400
> > ./xskgen -s 1400 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 116960000000 bits, took 1.189247 sec, 98.347946 gbps 8.408682 mpps
> > 
> > - baseline for 200
> > ./xskgen -s 200 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 20960000000 bits, took 0.421248 sec, 49.756913 gbps 23.738985 mpps
> > 
> > 3. Adding -M flag causes xskgen to reserve the metadata and fill it, but
> >     doesn't set XDP_TX_METADATA descriptor option.
> > 
> > - new baseline for 1400 (with only filling the metadata)
> > ./xskgen -M -s 1400 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 116960000000 bits, took 1.188767 sec, 98.387657 gbps 8.412077 mpps
> > 
> > - new baseline for 200 (with only filling the metadata)
> > ./xskgen -M -s 200 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 20960000000 bits, took 0.410213 sec, 51.095407 gbps 24.377579 mpps
> > (the numbers go sligtly up here, not really sure why, maybe some cache-related
> > side-effects?
> > 
> 
> Notice this change/improvement (23.7 to 24.4 Mpps) is only 1 nanosec.
>  - (1/24.377579-1/23.738985)*10^3 = -1.103499 nanosec
> 
> This 1 nanosec could be noise in your testlab.
 
Idk, it still doesn't make sense to me. I can consistently see this
difference with adding/removing -M flag :-/

> > 4. Next, I'm running the same test but with the commit that adds actual
> >     general infra to parse XDP_TX_METADATA (but no driver support).
> >     Essentially applying "xsk: add TX timestamp and TX checksum offload support"
> >     from this series. Numbers are the same.
> > 
> > - fill metadata for 1400
> > ./xskgen -M -s 1400 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 116960000000 bits, took 1.188430 sec, 98.415557 gbps 8.414463 mpps
> > 
> > - fill metadata for 200
> > ./xskgen -M -s 200 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 20960000000 bits, took 0.411559 sec, 50.928299 gbps 24.297853 mpps
> > 
> > - request metadata for 1400
> > ./xskgen -m -s 1400 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 116960000000 bits, took 1.188723 sec, 98.391299 gbps 8.412389 mpps
> > 
> > - request metadata for 200
> > ./xskgen -m -s 200 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000064 packets 20960134144 bits, took 0.411240 sec, 50.968131 gbps 24.316856 mpps
> > 
> > 5. Now, for the most interesting part, I'm adding mlx5 driver support.
> >     The mpps for 200 bytes case goes down from 23 mpps to 19 mpps, but
> >     _only_ when I enable the metadata. This looks like a side effect
> >     of me pushing extra metadata pointer via mlx5e_xdpi_fifo_push.
> >     Hence, this part is wrapped into 'if (xp_tx_metadata_enabled)'
> >     to not affect the existing non-metadata use-cases. Since this is not
> >     regressing existing workloads, I'm not spending any time trying to
> >     optimize it more (and leaving it up to mlx owners to purse if
> >     they see any good way to do it).
> > 
> > - same baseline
> > ./xskgen -s 1400 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 116960000000 bits, took 1.189434 sec, 98.332484 gbps 8.407360 mpps
> > 
> > ./xskgen -s 200 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000128 packets 20960268288 bits, took 0.425254 sec, 49.288821 gbps 23.515659 mpps
> > 
> > - fill metadata for 1400
> > ./xskgen -M -s 1400 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 116960000000 bits, took 1.189528 sec, 98.324714 gbps 8.406696 mpps
> > 
> > - fill metadata for 200
> > ./xskgen -M -s 200 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000128 packets 20960268288 bits, took 0.519085 sec, 40.379260 gbps 19.264914 mpps
> > 
> 
> This change from 23 mpps to 19 mpps is approx 10 nanosec
>  - (1/23.738985-1/19.264914)*10^3 = -9.78 nanosec
>  - (1/23.515659-1/19.264914)*10^3 = -9.38 nanosec
> 
> A 10 nanosec difference is more than noise.

Yeah, it's because the of way mlx5 cleans the tx queue via that extra
mlx5e_xdpi_fifo_push/mlx5e_xdpi_fifo_pop. As long as I comment this part
out (since it's technically only needed for the timestamp), the numbers
look better.

> > - request metadata for 1400
> > ./xskgen -m -s 1400 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000000 packets 116960000000 bits, took 1.189329 sec, 98.341165 gbps 8.408102 mpps
> > 
> > - request metadata for 200
> > ./xskgen -m -s 200 -b eth3 10:70:fd:48:10:77 10:70:fd:48:10:87 fe80::1270:fdff:fe48:1077 fe80::1270:fdff:fe48:1087 1 1
> > sent 10000128 packets 20960268288 bits, took 0.519929 sec, 40.313713 gbps 19.233642 mpps
> > 
> > Cc: Saeed Mahameed <[email-masked]>
> > 
> > Stanislav Fomichev (9):
> >    xsk: Support XDP_TX_METADATA_LEN
> >    xsk: add TX timestamp and TX checksum offload support
> >    tools: ynl: print xsk-features from the sample
> >    net/mlx5e: Implement AF_XDP TX timestamp and checksum offload
> >    selftests/xsk: Support XDP_TX_METADATA_LEN
> >    selftests/bpf: Add csum helpers
> >    selftests/bpf: Add TX side to xdp_metadata
> >    selftests/bpf: Add TX side to xdp_hw_metadata
> >    xsk: document XDP_TX_METADATA_LEN layout
> > 
> >   Documentation/netlink/specs/netdev.yaml       |  20 ++
> >   Documentation/networking/index.rst            |   1 +
> >   Documentation/networking/xsk-tx-metadata.rst  |  75 +++++++
> >   drivers/net/ethernet/mellanox/mlx5/core/en.h  |   4 +-
> >   .../net/ethernet/mellanox/mlx5/core/en/xdp.c  |  72 ++++++-
> >   .../net/ethernet/mellanox/mlx5/core/en/xdp.h  |  10 +-
> >   .../ethernet/mellanox/mlx5/core/en/xsk/tx.c   |  11 +-
> >   .../net/ethernet/mellanox/mlx5/core/en_main.c |   1 +
> >   include/linux/netdevice.h                     |  27 +++
> >   include/linux/skbuff.h                        |   5 +-
> >   include/net/xdp_sock.h                        |  61 ++++++
> >   include/net/xdp_sock_drv.h                    |  13 ++
> >   include/net/xsk_buff_pool.h                   |   6 +
> >   include/uapi/linux/if_xdp.h                   |  36 ++++
> >   include/uapi/linux/netdev.h                   |  16 ++
> >   net/core/netdev-genl.c                        |  12 +-
> >   net/xdp/xsk.c                                 |  61 ++++++
> >   net/xdp/xsk_buff_pool.c                       |   1 +
> >   net/xdp/xsk_queue.h                           |  19 +-
> >   tools/include/uapi/linux/if_xdp.h             |  50 ++++-
> >   tools/include/uapi/linux/netdev.h             |  15 ++
> >   tools/net/ynl/generated/netdev-user.c         |  19 ++
> >   tools/net/ynl/generated/netdev-user.h         |   3 +
> >   tools/net/ynl/samples/netdev.c                |   6 +
> >   tools/testing/selftests/bpf/network_helpers.h |  43 ++++
> >   .../selftests/bpf/prog_tests/xdp_metadata.c   |  31 ++-
> >   tools/testing/selftests/bpf/xdp_hw_metadata.c | 201 +++++++++++++++++-
> >   tools/testing/selftests/bpf/xsk.c             |  17 ++
> >   tools/testing/selftests/bpf/xsk.h             |   1 +
> >   29 files changed, 793 insertions(+), 44 deletions(-)
> >   create mode 100644 Documentation/networking/xsk-tx-metadata.rst
> > 
> 
> Thanks for working on this :-)
> --Jesper
>