Re: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support

Jesper Dangaard Brouer
2022-09-29T18:55:26Z

On 29/09/2022 17.52, Shenwei Wang wrote:
>
>> From: Jesper Dangaard Brouer <jbrouer@redhat.com>
>>
>> On 29/09/2022 15.26, Shenwei Wang wrote:
>>>
>>>> From: Andrew Lunn <andrew@lunn.ch>
>>>> Sent: Thursday, September 29, 2022 8:23 AM
>> [...]
>>>>
>>>>> I actually did some compare testing regarding the page pool for
>>>>> normal traffic. So far I don't see significant improvement in the
>>>>> current implementation. The performance for large packets improves a
>>>>> little, and the performance for small packets get a little worse.
>>>>
>>>> What hardware was this for? imx51? imx6? imx7 Vybrid? These all use the FEC.
>>>
>>> I tested on imx8qxp platform. It is ARM64.
>>
>> On mvneta driver/platform we saw huge speedup replacing:
>>
>> page_pool_release_page(rxq->page_pool, page); with
>> skb_mark_for_recycle(skb);
>>
>> As I mentioned: Today page_pool have SKB recycle support (you might have
>> looked at drivers that didn't utilize this yet), thus you don't need to release the
>> page (page_pool_release_page) here. Instead you could simply mark the SKB
>> for recycling, unless driver does some page refcnt tricks I didn't notice.
>>
>> On the mvneta driver/platform the DMA unmap (in page_pool_release_page)
>> was very expensive. This imx8qxp platform might have faster DMA unmap in
>> case is it cache-coherent.
>>
>> I would be very interested in knowing if skb_mark_for_recycle() helps on this
>> platform, for normal network stack performance.
>>
>
> Did a quick compare testing for the following 3 scenarios:

Thanks for doing this! :-)

> 1. original implementation
>
> shenwei@5810:~$ iperf -c 10.81.16.245 -w 2m -i 1
> ------------------------------------------------------------
> Client connecting to 10.81.16.245, TCP port 5001
> TCP window size: 416 KByte (WARNING: requested 1.91 MByte)
> ------------------------------------------------------------
> [ 1] local 10.81.17.20 port 49154 connected with 10.81.16.245 port 5001
> [ ID] Interval Transfer Bandwidth
> [ 1] 0.0000-1.0000 sec 104 MBytes 868 Mbits/sec
> [ 1] 1.0000-2.0000 sec 105 MBytes 878 Mbits/sec
> [ 1] 2.0000-3.0000 sec 105 MBytes 881 Mbits/sec
> [ 1] 3.0000-4.0000 sec 105 MBytes 879 Mbits/sec
> [ 1] 4.0000-5.0000 sec 105 MBytes 878 Mbits/sec
> [ 1] 5.0000-6.0000 sec 105 MBytes 878 Mbits/sec
> [ 1] 6.0000-7.0000 sec 104 MBytes 875 Mbits/sec
> [ 1] 7.0000-8.0000 sec 104 MBytes 875 Mbits/sec
> [ 1] 8.0000-9.0000 sec 104 MBytes 873 Mbits/sec
> [ 1] 9.0000-10.0000 sec 104 MBytes 875 Mbits/sec
> [ 1] 0.0000-10.0073 sec 1.02 GBytes 875 Mbits/sec
>
> 2. Page pool with page_pool_release_page
>
> shenwei@5810:~$ iperf -c 10.81.16.245 -w 2m -i 1
> ------------------------------------------------------------
> Client connecting to 10.81.16.245, TCP port 5001
> TCP window size: 416 KByte (WARNING: requested 1.91 MByte)
> ------------------------------------------------------------
> [ 1] local 10.81.17.20 port 35924 connected with 10.81.16.245 port 5001
> [ ID] Interval Transfer Bandwidth
> [ 1] 0.0000-1.0000 sec 101 MBytes 849 Mbits/sec
> [ 1] 1.0000-2.0000 sec 102 MBytes 860 Mbits/sec
> [ 1] 2.0000-3.0000 sec 102 MBytes 860 Mbits/sec
> [ 1] 3.0000-4.0000 sec 102 MBytes 859 Mbits/sec
> [ 1] 4.0000-5.0000 sec 103 MBytes 863 Mbits/sec
> [ 1] 5.0000-6.0000 sec 103 MBytes 864 Mbits/sec
> [ 1] 6.0000-7.0000 sec 103 MBytes 863 Mbits/sec
> [ 1] 7.0000-8.0000 sec 103 MBytes 865 Mbits/sec
> [ 1] 8.0000-9.0000 sec 103 MBytes 862 Mbits/sec
> [ 1] 9.0000-10.0000 sec 102 MBytes 856 Mbits/sec
> [ 1] 0.0000-10.0246 sec 1.00 GBytes 858 Mbits/sec
>
>
> 3. page pool with skb_mark_for_recycle
>
> shenwei@5810:~$ iperf -c 10.81.16.245 -w 2m -i 1
> ------------------------------------------------------------
> Client connecting to 10.81.16.245, TCP port 5001
> TCP window size: 416 KByte (WARNING: requested 1.91 MByte)
> ------------------------------------------------------------
> [ 1] local 10.81.17.20 port 42724 connected with 10.81.16.245 port 5001
> [ ID] Interval Transfer Bandwidth
> [ 1] 0.0000-1.0000 sec 111 MBytes 931 Mbits/sec
> [ 1] 1.0000-2.0000 sec 112 MBytes 935 Mbits/sec
> [ 1] 2.0000-3.0000 sec 111 MBytes 934 Mbits/sec
> [ 1] 3.0000-4.0000 sec 111 MBytes 934 Mbits/sec
> [ 1] 4.0000-5.0000 sec 111 MBytes 934 Mbits/sec
> [ 1] 5.0000-6.0000 sec 112 MBytes 935 Mbits/sec
> [ 1] 6.0000-7.0000 sec 111 MBytes 934 Mbits/sec
> [ 1] 7.0000-8.0000 sec 111 MBytes 933 Mbits/sec
> [ 1] 8.0000-9.0000 sec 112 MBytes 935 Mbits/sec
> [ 1] 9.0000-10.0000 sec 111 MBytes 933 Mbits/sec
> [ 1] 0.0000-10.0069 sec 1.09 GBytes 934 Mbits/sec

This is a very significant performance improvement (page pool with
skb_mark_for_recycle). This is very close to the max goodput for a
1Gbit/s link.

> For small packet size (64 bytes), all three cases have almost the same result:
>

To me this indicate, that the DMA map/unmap operations on this platform
are indeed more expensive on larger packets. Given this is what
page_pool does, keeping the DMA mapping intact when recycling.

Driver still need DMA-sync, although I notice you set page_pool feature
flag PP_FLAG_DMA_SYNC_DEV, this is good as page_pool will try to reduce
sync size where possible. E.g. in this SKB case will reduce the DMA-sync
to the max_len=FEC_ENET_RX_FRSIZE which should also help on performance.

> shenwei@5810:~$ iperf -c 10.81.16.245 -w 2m -i 1 -l 64
> ------------------------------------------------------------
> Client connecting to 10.81.16.245, TCP port 5001
> TCP window size: 416 KByte (WARNING: requested 1.91 MByte)
> ------------------------------------------------------------
> [ 1] local 10.81.17.20 port 58204 connected with 10.81.16.245 port 5001
> [ ID] Interval Transfer Bandwidth
> [ 1] 0.0000-1.0000 sec 36.9 MBytes 309 Mbits/sec
> [ 1] 1.0000-2.0000 sec 36.6 MBytes 307 Mbits/sec
> [ 1] 2.0000-3.0000 sec 36.6 MBytes 307 Mbits/sec
> [ 1] 3.0000-4.0000 sec 36.5 MBytes 307 Mbits/sec
> [ 1] 4.0000-5.0000 sec 37.1 MBytes 311 Mbits/sec
> [ 1] 5.0000-6.0000 sec 37.2 MBytes 312 Mbits/sec
> [ 1] 6.0000-7.0000 sec 37.1 MBytes 311 Mbits/sec
> [ 1] 7.0000-8.0000 sec 37.1 MBytes 311 Mbits/sec
> [ 1] 8.0000-9.0000 sec 37.1 MBytes 312 Mbits/sec
> [ 1] 9.0000-10.0000 sec 37.2 MBytes 312 Mbits/sec
> [ 1] 0.0000-10.0097 sec 369 MBytes 310 Mbits/sec
>
> Regards,
> Shenwei
>
>
>>>> By small packets, do you mean those under the copybreak limit?
>>>>
>>>> Please provide some benchmark numbers with your next patchset.
>>>
>>> Yes, the packet size is 64 bytes and it is under the copybreak limit.
>>> As the impact is not significant, I would prefer to remove the
>>> copybreak logic.
>>
>> +1 to removing this logic if possible, due to maintenance cost.
>>
>> --Jesper
>