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From: Jesper Dangaard Brouer <jbrouer@redhat.com>
To: Stanislav Fomichev <sdf@google.com>
Cc: brouer@redhat.com, bpf@vger.kernel.org,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	netdev@vger.kernel.org, martin.lau@kernel.org, ast@kernel.org,
	daniel@iogearbox.net, alexandr.lobakin@intel.com,
	larysa.zaremba@intel.com, xdp-hints@xdp-project.net,
	yoong.siang.song@intel.com, intel-wired-lan@lists.osuosl.org,
	pabeni@redhat.com, jesse.brandeburg@intel.com, kuba@kernel.org,
	edumazet@google.com, john.fastabend@gmail.com, hawk@kernel.org,
	davem@davemloft.net
Subject: [xdp-hints] Re: [PATCH bpf-next V2 5/5] selftests/bpf: xdp_hw_metadata track more timestamps
Date: Wed, 19 Apr 2023 18:41:07 +0200	[thread overview]
Message-ID: <925c8354-f3ba-53fb-3950-ec02d41a12a7@redhat.com> (raw)
In-Reply-To: <ZD7HJ3hdDdOSm/lK@google.com>



On 18/04/2023 18.36, Stanislav Fomichev wrote:
> On 04/18, 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.
>>
[...]

>> More explanation of the output and how this can be used to identify
>> clock drift for the HW clock can be seen here[1]:
>>
>> [1]https://github.com/xdp-project/xdp-project/blob/master/areas/hints/xdp_hints_kfuncs02_driver_igc.org
>>
>> Signed-off-by: Jesper Dangaard Brouer<brouer@redhat.com>
> Acked-by: Stanislav Fomichev<sdf@google.com>
> 
>> ---
>>   .../testing/selftests/bpf/progs/xdp_hw_metadata.c  |    4 +-
>>   tools/testing/selftests/bpf/xdp_hw_metadata.c      |   47 ++++++++++++++++++--
>>   tools/testing/selftests/bpf/xdp_metadata.h         |    1
>>   3 files changed, 46 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
>> index e1c787815e44..b2dfd7066c6e 100644
>> --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
>> +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
>> @@ -77,7 +77,9 @@ int rx(struct xdp_md *ctx)
>>   	}
>>   
>>   	err = bpf_xdp_metadata_rx_timestamp(ctx, &meta->rx_timestamp);
>> -	if (err)
> [..]
> 
>> +	if (!err)
>> +		meta->xdp_timestamp = bpf_ktime_get_tai_ns();
> nit: why not set it unconditionally?

Because userspace application doesn't use it for anything, when
meta->rx_timestamp is zero.

--Jesper


  reply	other threads:[~2023-04-19 16:41 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-04-18 13:30 [xdp-hints] [PATCH bpf-next V2 0/5] XDP-hints: XDP kfunc metadata for driver igc Jesper Dangaard Brouer
2023-04-18 13:30 ` [xdp-hints] [PATCH bpf-next V2 1/5] igc: enable and fix RX hash usage by netstack Jesper Dangaard Brouer
2023-04-23 14:46   ` [xdp-hints] " John Fastabend
2023-04-24 14:20     ` Jesper Dangaard Brouer
2023-04-24 19:17       ` John Fastabend
2023-04-25  8:43         ` Jesper Dangaard Brouer
2023-04-25  9:40           ` [xdp-hints] Re: [Intel-wired-lan] " Neftin, Sasha
2023-04-27 17:00           ` [xdp-hints] " Daniel Borkmann
2023-04-28 10:13             ` Jesper Dangaard Brouer
2023-04-18 13:30 ` [xdp-hints] [PATCH bpf-next V2 2/5] igc: add igc_xdp_buff wrapper for xdp_buff in driver Jesper Dangaard Brouer
2023-04-18 13:30 ` [xdp-hints] [PATCH bpf-next V2 3/5] igc: add XDP hints kfuncs for RX hash Jesper Dangaard Brouer
2023-04-18 13:30 ` [xdp-hints] [PATCH bpf-next V2 4/5] igc: add XDP hints kfuncs for RX timestamp Jesper Dangaard Brouer
2023-04-18 13:31 ` [xdp-hints] [PATCH bpf-next V2 5/5] selftests/bpf: xdp_hw_metadata track more timestamps Jesper Dangaard Brouer
2023-04-18 16:36   ` [xdp-hints] " Stanislav Fomichev
2023-04-19 16:41     ` Jesper Dangaard Brouer [this message]
2023-04-18 14:53 ` [xdp-hints] Re: [PATCH bpf-next V2 0/5] XDP-hints: XDP kfunc metadata for driver igc Song, Yoong Siang
2023-04-21 14:52   ` Daniel Borkmann
2023-04-24  2:14     ` Song, Yoong Siang
2023-04-27 17:00 ` patchwork-bot+netdevbpf

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