netdev - Re: [PATCH net-next v4 0/6] sfc: Add XDP support

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Date:   Thu, 31 Oct 2019 16:18:04 -0600
From:   David Ahern <dsahern@...il.com>
To:     Charles McLachlan <cmclachlan@...arflare.com>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, linux-net-drivers@...arflare.com,
        brouer@...hat.com
Subject: Re: [PATCH net-next v4 0/6] sfc: Add XDP support

On 10/31/19 4:21 AM, Charles McLachlan wrote:
> Supply the XDP callbacks in netdevice ops that enable lower level processing
> of XDP frames.
> 
> Changes in v4:
> - Handle the failure to send some frames in efx_xdp_tx_buffers() properly.
> 
> Changes in v3:
> - Fix a BUG_ON when trying to allocate piobufs to xdp queues.
> - Add a missed trace_xdp_exception.
> 
> Changes in v2:
> - Use of xdp_return_frame_rx_napi() in tx.c
> - Addition of xdp_rxq_info_valid and xdp_rxq_info_failed to track when
>   xdp_rxq_info failures occur.
> - Renaming of rc to err and more use of unlikely().
> - Cut some duplicated code and fix an array overrun.
> - Actually increment n_rx_xdp_tx when packets are transmitted.
> 

Something is up with this version versus v2. I am seeing a huge
performance drop with my L2 forwarding program - something I was not
seeing with v2 and I do not see with the experimental version of XDP in
the out of tree sfc driver.

Without XDP:

$ netperf -H 10.39.16.7 -l 30 -t TCP_STREAM
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
10.39.16.7 () port 0 AF_INET : demo
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    30.00    9386.73


With XDP

$ netperf -H 10.39.16.7 -l 30 -t TCP_STREAM
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
10.39.16.7 () port 0 AF_INET : demo
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    30.01     384.11


Prior versions was showing throughput of at least 4000 (depends on the
test and VM setup).