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ntp: fix presend in interleaved mode

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The presend option in interleaved mode uses two presend requests instead
of one to get an interleaved response from servers like chrony which
delay the first interleaved response due to an optimization saving
timestamps only for clients actually using the interleaved mode.

After commit 0ae6f2485b ("ntp: don't use first response in interleaved
mode") the first interleaved response following the two presend
responses in basic mode is dropped as the preferred set of timestamps
minimizing error in delay was already used by the second sample in
basic mode. There are only three responses in the burst and no sample is
accumulated.

Increasing the number of presend requests to three to get a fourth
sample would be wasteful. Instead, allow reusing timestamps of the
second presend sample in basic mode, which is never accumulated.

Reported-by: Aaron Thompson
Fixes: 0ae6f2485b ("ntp: don't use first response in interleaved mode")
This commit is contained in:
Miroslav Lichvar 2023-11-21 07:51:37 +01:00
parent 9c6eaccc32
commit 2d2642bb82
2 changed files with 26 additions and 1 deletions
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2
ntp_core.c
View file

@ -2302,7 +2302,7 @@ process_response(NCR_Instance inst, int saved, NTP_Local_Address *local_addr,
inst->local_tx.net_correction = net_correction; inst->local_tx.net_correction = net_correction;
/* Don't use the same set of timestamps for the next sample */ /* Don't use the same set of timestamps for the next sample */
if (interleaved_packet) if (interleaved_packet || inst->presend_done > 0)
inst->prev_local_tx = inst->local_tx; inst->prev_local_tx = inst->local_tx;
else else
zero_local_timestamp(&inst->prev_local_tx); zero_local_timestamp(&inst->prev_local_tx);

25
test/simulation/114-presend
View file

@ -23,4 +23,29 @@ check_source_selection || test_fail
check_packet_interval || test_fail check_packet_interval || test_fail
check_sync || test_fail check_sync || test_fail
limit=10
base_delay=$default_base_delay
client_conf="logdir tmp
log measurements"
client_server_options="presend 5"
run_test || test_fail
check_chronyd_exit || test_fail
check_packet_interval || test_fail
check_file_messages "20.*123\.1.* 111 111 0111" 1 1 measurements.log || test_fail
check_file_messages "20.*123\.1.* 111 111 1111" 1 1 measurements.log || test_fail
rm -f tmp/measurements.log
client_server_options="presend 5 xleave"
run_test || test_fail
check_chronyd_exit || test_fail
check_packet_interval || test_fail
check_file_messages "20.*123\.1.* 111 111 0111" 2 2 measurements.log || test_fail
check_file_messages "20.*123\.1.* 111 111 1111" 1 1 measurements.log || test_fail
rm -f tmp/measurements.log
test_pass test_pass