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

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Date:   Fri, 23 Aug 2019 08:10:25 +0200
From:   Björn Töpel <bjorn.topel@...el.com>
To:     William Tu <u9012063@...il.com>,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     Ilya Maximets <i.maximets@...sung.com>,
        Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        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 <intel-wired-lan@...ts.osuosl.org>,
        Eelco Chaudron <echaudro@...hat.com>
Subject: Re: [PATCH net v3] ixgbe: fix double clean of tx descriptors with xdp

On 2019-08-22 19:32, William Tu wrote:
> On Thu, Aug 22, 2019 at 10:21 AM Alexander Duyck
> <alexander.duyck@...il.com> wrote:
>>
>> On Thu, Aug 22, 2019 at 10:12 AM Ilya Maximets <i.maximets@...sung.com> 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(-)
>>
>> Thanks for addressing my concerns.
>>
>> Acked-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> 
> Thanks.
> 
> Tested-by: William Tu <u9012063@...il.com>
> 

Will, thanks for testing! For this patch, did you notice any performance
degradation?


Cheers,
Björn