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Tony Nguyen says:
====================
igc: TX timestamping fixes
This is the fixes part of the series intended to add support for using
the 4 timestamp registers present in i225/i226.
Moving the timestamp handling to be inline with the interrupt handling
has the advantage of improving the TX timestamping retrieval latency,
here are some numbers using ntpperf:
Before:
$ sudo ./ntpperf -i enp3s0 -m 10:22:22:22:22:21 -d 192.168.1.3 -s 172.18.0.0/16 -I -H -o -37
| responses | TX timestamp offset (ns)
rate clients | lost invalid basic xleave | min mean max stddev
1000 100 0.00% 0.00% 0.00% 100.00% -56 +9 +52 19
1500 150 0.00% 0.00% 0.00% 100.00% -40 +30 +75 22
2250 225 0.00% 0.00% 0.00% 100.00% -11 +29 +72 15
3375 337 0.00% 0.00% 0.00% 100.00% -18 +40 +88 22
5062 506 0.00% 0.00% 0.00% 100.00% -19 +23 +77 15
7593 759 0.00% 0.00% 0.00% 100.00% +7 +47 +5168 43
11389 1138 0.00% 0.00% 0.00% 100.00% -11 +41 +5240 39
17083 1708 0.00% 0.00% 0.00% 100.00% +19 +60 +5288 50
25624 2562 0.00% 0.00% 0.00% 100.00% +1 +56 +5368 58
38436 3843 0.00% 0.00% 0.00% 100.00% -84 +12 +8847 66
57654 5765 0.00% 0.00% 100.00% 0.00%
86481 8648 0.00% 0.00% 100.00% 0.00%
129721 12972 0.00% 0.00% 100.00% 0.00%
194581 16384 0.00% 0.00% 100.00% 0.00%
291871 16384 27.35% 0.00% 72.65% 0.00%
437806 16384 50.05% 0.00% 49.95% 0.00%
After:
$ sudo ./ntpperf -i enp3s0 -m 10:22:22:22:22:21 -d 192.168.1.3 -s 172.18.0.0/16 -I -H -o -37
| responses | TX timestamp offset (ns)
rate clients | lost invalid basic xleave | min mean max stddev
1000 100 0.00% 0.00% 0.00% 100.00% -44 +0 +61 19
1500 150 0.00% 0.00% 0.00% 100.00% -6 +39 +81 16
2250 225 0.00% 0.00% 0.00% 100.00% -22 +25 +69 15
3375 337 0.00% 0.00% 0.00% 100.00% -28 +15 +56 14
5062 506 0.00% 0.00% 0.00% 100.00% +7 +78 +143 27
7593 759 0.00% 0.00% 0.00% 100.00% -54 +24 +144 47
11389 1138 0.00% 0.00% 0.00% 100.00% -90 -33 +28 21
17083 1708 0.00% 0.00% 0.00% 100.00% -50 -2 +35 14
25624 2562 0.00% 0.00% 0.00% 100.00% -62 +7 +66 23
38436 3843 0.00% 0.00% 0.00% 100.00% -33 +30 +5395 36
57654 5765 0.00% 0.00% 100.00% 0.00%
86481 8648 0.00% 0.00% 100.00% 0.00%
129721 12972 0.00% 0.00% 100.00% 0.00%
194581 16384 19.50% 0.00% 80.50% 0.00%
291871 16384 35.81% 0.00% 64.19% 0.00%
437806 16384 55.40% 0.00% 44.60% 0.00%
During this series, and to show that as is always the case, things are
never easy as they should be, a hardware issue was found, and it took
some time to find the workaround(s). The bug and workaround are better
explained in patch 4/4.
Note: the workaround has a simpler alternative, but it would involve
adding support for the other timestamp registers, and only using the
TXSTMP{H/L}_0 as a way to clear the interrupt. But I feel bad about
throwing this kind of resources away. Didn't test this extensively but
it should work.
Also, as Marc Kleine-Budde suggested, after some consensus is reached
on this series, most parts of it will be proposed for igb.
* '1GbE' of git://git.kernel.org/pub/scm/linux/kernel/git/tnguy/net-queue:
igc: Work around HW bug causing missing timestamps
igc: Retrieve TX timestamp during interrupt handling
igc: Check if hardware TX timestamping is enabled earlier
igc: Fix race condition in PTP tx code
====================
Link: https://lore.kernel.org/r/20230622165244.2202786-1-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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