[v2] doc/mlx5: add timestamp upper limitation description
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Message ID 1595865064-12892-1-git-send-email-viacheslavo@mellanox.com
State Superseded, archived
Delegated to: Thomas Monjalon
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  • [v2] doc/mlx5: add timestamp upper limitation description
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ci/Intel-compilation success Compilation OK
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ci/checkpatch warning coding style issues

Commit Message

Slava Ovsiienko July 27, 2020, 3:51 p.m. UTC
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 scheduled at all (is being
sent without any wait).

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
---
v1->v2: typo fix

 doc/guides/nics/mlx5.rst | 7 +++++++
 1 file changed, 7 insertions(+)

Patch
diff mbox series

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index 90202c0..b9bd3db 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -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