netdev - Re: [PATCH net v3] ixgbe: fix double clean of tx descriptors with xdp

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Message-ID: <660415CE-6748-4749-84D6-7007F69D8EFB@redhat.com>
Date:   Fri, 23 Aug 2019 14:10:45 +0200
From:   "Eelco Chaudron" <echaudro@...hat.com>
To:     "Ilya Maximets" <i.maximets@...sung.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        "Björn Töpel" <bjorn.topel@...el.com>,
        "Magnus Karlsson" <magnus.karlsson@...el.com>,
        "Jakub Kicinski" <jakub.kicinski@...ronome.com>,
        "Alexei Starovoitov" <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        "Jeff Kirsher" <jeffrey.t.kirsher@...el.com>,
        intel-wired-lan@...ts.osuosl.org,
        "William Tu" <u9012063@...il.com>,
        "Alexander Duyck" <alexander.duyck@...il.com>
Subject: Re: [PATCH net v3] ixgbe: fix double clean of tx descriptors with xdp



On 22 Aug 2019, at 19:12, Ilya Maximets wrote:

> Tx code doesn't clear the descriptors' status after cleaning.
> So, if the budget is larger than number of used elems in a ring, some
> descriptors will be accounted twice and xsk_umem_complete_tx will move
> prod_tail far beyond the prod_head breaking the completion queue ring.
>
> Fix that by limiting the number of descriptors to clean by the number
> of used descriptors in the tx ring.
>
> 'ixgbe_clean_xdp_tx_irq()' function refactored to look more like
> 'ixgbe_xsk_clean_tx_ring()' since we're allowed to directly use
> 'next_to_clean' and 'next_to_use' indexes.
>
> Fixes: 8221c5eba8c1 ("ixgbe: add AF_XDP zero-copy Tx support")
> Signed-off-by: Ilya Maximets <i.maximets@...sung.com>
> ---
>
> Version 3:
>   * Reverted some refactoring made for v2.
>   * Eliminated 'budget' for tx clean.
>   * prefetch returned.
>
> Version 2:
>   * 'ixgbe_clean_xdp_tx_irq()' refactored to look more like
>     'ixgbe_xsk_clean_tx_ring()'.
>
>  drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 29 
> ++++++++------------
>  1 file changed, 11 insertions(+), 18 deletions(-)
>

Did some test with and without the fix applied. For PVP the results are 
a little different depending on the packet size (note this is a single 
run, no deviation).
For the same physical port in and out it’s faster! Note this was OVS 
AF_XDP using a XENA tester at 10G wire speed.


+--------------------------------------------------------------------------------+
| Physical to Virtual to Physical test, L3 flows[port redirect]          
         |
+-----------------+--------------------------------------------------------------+
|                 | Packet size                                          
         |
+-----------------+--------+--------+--------+--------+--------+--------+--------+
| Number of flows |   64   |  128   |  256   |  512   |  768   |  1024  
|  1514  |
+-----------------+--------+--------+--------+--------+--------+--------+--------+
| [NO FIX]   1000 | 739161 | 700091 | 690034 | 659894 | 618128 | 594223 
| 537504 |
+-----------------+--------+--------+--------+--------+--------+--------+--------+
| [FIX]      1000 | 742317 | 708391 | 689952 | 658034 | 626056 | 587653 
| 530885 |
+-----------------+--------+--------+--------+--------+--------+--------+--------+

+--------------------------------------------------------------------------------------+
| Physical loopback test, L3 flows[port redirect]                        
               |
+-----------------+--------------------------------------------------------------------+
|                 | Packet size                                          
               |
+-----------------+---------+---------+---------+---------+---------+---------+--------+
| Number of flows |   64    |   128   |   256   |   512   |   768   |  
1024   |  1514  |
+-----------------+---------+---------+---------+---------+---------+---------+--------+
| [NO FIX]   1000 | 2573298 | 2227578 | 2514318 | 2298204 | 1081861 | 
1015173 | 788081 |
+-----------------+---------+---------+---------+---------+---------+---------+--------+
| [FIX]      1000 | 3343188 | 3234993 | 3151833 | 2349597 | 1586276 | 
1197304 | 814854 |
+-----------------+---------+---------+---------+---------+---------+---------+--------+


Tested-by: Eelco Chaudron <echaudro@...hat.com>