doc/mlx5: add timestamp upper limitaion description
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Commit Message
Add description about Tx scheduling timstamp upper limit.
It timstamp exceed the value it is marked by PMD as being
into "too-distant-future" and not sheduled at all (is being
sent without any wait).
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
---
doc/guides/nics/mlx5.rst | 7 +++++++
1 file changed, 7 insertions(+)
@@ -253,6 +253,13 @@ Limitations
reported via device xstats to assist applications to detect the
time-related problems.
+ The timestamp upper "too-distant-future" limit at the moment of invoking
+ the tx_burst routine can be estimated as ``tx_pp`` devarog (in nanoseconds)
+ multiplied by 2^23. Please note, for the testpmd txonly testcase the limit
+ is deduced from the expression::
+
+ (n_tx_descriptors / burst_size + 1) * inter_burst_gap
+
There is no any packet reordering according timestamps is supposed,
neither within packet burst, nor between packets, it is an entirely
application responsibility to generate packets and its timestamps