[dpdk-dev] [PATCH v3] doc: add timestamp upper limitation in mlx5 guide

[Thomas Monjalon <thomas@monjalon.net>]

From: Viacheslav Ovsiienko <viacheslavo@mellanox.com>

Add description about Tx scheduling timestamp upper limit.
If timestamp exceed 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>
---
v2: typo fix
v3: more typos fixed and small rewording
---
 doc/guides/nics/mlx5.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index 90202c0bbb..211c0c5a6c 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -253,6 +253,14 @@ 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`` 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,
   neither within packet burst, nor between packets, it is an entirely
   application responsibility to generate packets and its timestamps
-- 
2.27.0