netdev - RE: [PATCH bpf-next V1 5/5] selftests/bpf: xdp_hw

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Message-ID: <PH0PR11MB5830D771AA05F28675173A42D89D9@PH0PR11MB5830.namprd11.prod.outlook.com>
Date:   Tue, 18 Apr 2023 06:07:58 +0000
From:   "Song, Yoong Siang" <yoong.siang.song@...el.com>
To:     "Kanzenbach, Kurt" <kurt.kanzenbach@...utronix.de>,
        "Brouer, Jesper" <brouer@...hat.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "Stanislav Fomichev" <sdf@...gle.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>
CC:     "Brouer, Jesper" <brouer@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "martin.lau@...nel.org" <martin.lau@...nel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "Lobakin, Aleksander" <aleksander.lobakin@...el.com>,
        "Zaremba, Larysa" <larysa.zaremba@...el.com>,
        "xdp-hints@...-project.net" <xdp-hints@...-project.net>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "hawk@...nel.org" <hawk@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: RE: [PATCH bpf-next V1 5/5] selftests/bpf: xdp_hw_metadata track more
 timestamps

On Monday, April 17, 2023 11:32 PM, Kurt Kanzenbach <kurt.kanzenbach@...utronix.de> wrote:
>On Mon Apr 17 2023, Jesper Dangaard Brouer wrote:
>> To correlate the hardware RX timestamp with something, add tracking of
>> two software timestamps both clock source CLOCK_TAI (see description
>> in man clock_gettime(2)).
>>
>> XDP metadata is extended with xdp_timestamp for capturing when XDP
>> received the packet. Populated with BPF helper bpf_ktime_get_tai_ns().
>> I could not find a BPF helper for getting CLOCK_REALTIME, which would
>> have been preferred. In userspace when AF_XDP sees the packet another
>> software timestamp is recorded via clock_gettime() also clock source
>> CLOCK_TAI.
>>
>> Example output shortly after loading igc driver:
>>
>>   poll: 1 (0) skip=1 fail=0 redir=2
>>   xsk_ring_cons__peek: 1
>>   0x12557a8: rx_desc[1]->addr=100000000009000 addr=9100 comp_addr=9000
>>   rx_hash: 0x82A96531 with RSS type:0x1
>>   rx_timestamp:  1681740540304898909 (sec:1681740540.3049)
>>   XDP RX-time:   1681740577304958316 (sec:1681740577.3050) delta
>sec:37.0001 (37000059.407 usec)
>>   AF_XDP time:   1681740577305051315 (sec:1681740577.3051) delta
>sec:0.0001 (92.999 usec)
>>   0x12557a8: complete idx=9 addr=9000
>>
>> The first observation is that the 37 sec difference between RX HW vs
>> XDP timestamps, which indicate hardware is likely clock source
>> CLOCK_REALTIME, because (as of this writing) CLOCK_TAI is initialised
>> with a 37 sec offset.
>
>Maybe I'm missing something here, but in order to compare the hardware with
>software timestamps (e.g., by using bpf_ktime_get_tai_ns()) the time sources
>have to be synchronized by using something like phc2sys. That should make them
>comparable within reasonable range (nanoseconds).
>
>Thanks,
>Kurt

Tested-by: Song Yoong Siang <yoong.siang.song@...el.com>

I tested this patchset by using I226-LM (rev 04) NIC on Tiger Lake Platform.
I use testptp selftest tool to make sure PHC is almost same as system clock.
Below are the detail of test steps and result.

1. Run xdp_hw_metadata tool.
   @DUT: sudo ./xdp_hw_metadata eth0

2. Enable Rx HWTS for all incoming packets. Note: This step is not needed if
   https://lore.kernel.org/all/20230414154902.2950535-1-yoong.siang.song@intel.com/
   bug fix patch is applied to the igc driver.
   @DUT: sudo hwstamp_ctl -i eth0 -r 1

3. Set the ptp clock time from the system time using testptp tool.
   @DUT: sudo ./testptp -d /dev/ptp0 -s

4. Send UDP packet with 9091 port from link partner immediately after step 3.
   @LinkPartner: echo -n xdp | nc -u -q1 <Destination IPv4 addr> 9091

Result:
   poll: 1 (0) skip=1 fail=0 redir=1
   xsk_ring_cons__peek: 1
   0x5626248d16d0: rx_desc[0]->addr=100000000008000 addr=8100 comp_addr=8000
   rx_hash: 0x35E1B60E with RSS type:0x1
   rx_timestamp:  1677762195217129600 (sec:1677762195.2171)
   XDP RX-time:   1677762195217202099 (sec:1677762195.2172) delta sec:0.0001 (72.499 usec)
   AF_XDP time:   1677762195217231775 (sec:1677762195.2172) delta sec:0.0000 (29.676 usec)
   0x5626248d16d0: complete idx=8 addr=8000