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Date:   Tue, 4 Oct 2022 13:21:49 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Shenwei Wang <shenwei.wang@....com>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     brouer@...hat.com, Joakim Zhang <qiangqing.zhang@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Björn Töpel <bjorn@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: Re: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support


On 03/10/2022 14.49, Shenwei Wang wrote:
> Hi Jesper,
> 
>>>> On mvneta driver/platform we saw huge speedup replacing:
>>>>
>>>>      page_pool_release_page(rxq->page_pool, page); with
>>>>      skb_mark_for_recycle(skb);
>>>>
> 
> After replacing the page_pool_release_page with the
> skb_mark_for_recycle, I found something confused me a little in the
> testing result. >
> I tested with the sample app of "xdpsock" under two modes: 
>  1. Native (xdpsock -i eth0). 
>  2. Skb-mode (xdpsock -S -i eth0).
Great that you are also testing AF_XDP, but do you have a particular
use-case that needs AF_XDP on this board?

What packet size are used in below results?

> The following are the testing result:
 >
>       With page_pool_release_page (pps)  With skb_mark_for_recycle (pps)
> 
>   SKB-Mode                          90K                            200K
>   Native                           190K                            190K
> 

The default AF_XDP test with xdpsock is rxdrop IIRC.

Can you test the normal XDP code path and do a XDP_DROP test via the
samples tool 'xdp_rxq_info' and cmdline:

   sudo ./xdp_rxq_info --dev eth42 --act XDP_DROP --read

And then same with --skb-mode

> The skb_mark_for_recycle solution boosted the performance of SKB-Mode
> to 200K+ PPS. That is even higher than the performance of Native
> solution.  Is this result reasonable? Do you have any clue why the
> SKB-Mode performance can go higher than that of Native one?
I might be able to explain this (Cc. AF_XDP maintainers to keep me honest).

When you say "native" *AF_XDP* that isn't Zero-Copy AF_XDP.

Sure, XDP runs in native driver mode and redirects the raw frames into 
the AF_XDP socket, but as this isn't zero-copy AF_XDP. Thus, the packets 
needs to be copied into the AF_XDP buffers.

As soon as the frame or SKB (for generic XDP) have been copied it is 
released/freed by AF_XDP/xsk code (either via xdp_return_buff() or 
consume_skb()). Thus, it looks like it really pays off to recycle the 
frame via page_pool, also for the SKB consume_skb() case.

I am still a little surprised that to can be faster than native AF_XDP, 
as the SKB-mode ("XDP-generic") needs to call through lot more software 
layers and convert the SKB to look like an xdp_buff.

--Jesper



>> -----Original Message-----
>> From: Jesper Dangaard Brouer <jbrouer@...hat.com>
>> Sent: Thursday, September 29, 2022 1:55 PM
>> To: Shenwei Wang <shenwei.wang@....com>; Jesper Dangaard Brouer
>> <jbrouer@...hat.com>; Andrew Lunn <andrew@...n.ch>
>> Cc: brouer@...hat.com; Joakim Zhang <qiangqing.zhang@....com>; David S.
>> Miller <davem@...emloft.net>; Eric Dumazet <edumazet@...gle.com>; Jakub
>> Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>; Alexei
>> Starovoitov <ast@...nel.org>; Daniel Borkmann <daniel@...earbox.net>;
>> Jesper Dangaard Brouer <hawk@...nel.org>; John Fastabend
>> <john.fastabend@...il.com>; netdev@...r.kernel.org; linux-
>> kernel@...r.kernel.org; imx@...ts.linux.dev
>> Subject: Re: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support
>>
>> Caution: EXT Email
>>
>> On 29/09/2022 17.52, Shenwei Wang wrote:
>>>
>>>> From: Jesper Dangaard Brouer <jbrouer@...hat.com>
>>>>
>>>> On 29/09/2022 15.26, Shenwei Wang wrote:
>>>>>
>>>>>> From: Andrew Lunn <andrew@...n.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@...0:~$ 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@...0:~$ 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@...0:~$ 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@...0:~$ 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
>>>
> 

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