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doc: add timestamp upper limitation in mlx5 guide

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Add description about Tx scheduling timestamp upper limit.
If timestamp exceeds the value, it is marked by PMD as being
into "too-distant-future" and not scheduled at all
(is being sent without any wait).

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
This commit is contained in:
Viacheslav Ovsiienko 2020-07-27 15:51:04 +00:00 committed by Thomas Monjalon
parent 38a5704629
commit b5f615612a
1 changed files with 8 additions and 0 deletions
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8
doc/guides/nics/mlx5.rst
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@ -253,6 +253,14 @@ Limitations
reported via device xstats to assist applications to detect the reported via device xstats to assist applications to detect the
time-related problems. 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`` option (in nanoseconds) multiplied by 2^23.
Please note, for the testpmd txonly mode,
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, There is no any packet reordering according timestamps is supposed,
neither within packet burst, nor between packets, it is an entirely neither within packet burst, nor between packets, it is an entirely
application responsibility to generate packets and its timestamps application responsibility to generate packets and its timestamps