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From: Thomas Monjalon <thomas@monjalon.net>
To: dev@dpdk.org
Cc: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Subject: [dpdk-dev] [PATCH v3] doc: add timestamp upper limitation in mlx5 guide
Date: Wed,  5 Aug 2020 17:26:10 +0200
Message-ID: <20200805152610.277087-1-thomas@monjalon.net> (raw)
In-Reply-To: <1595865064-12892-1-git-send-email-viacheslavo@mellanox.com>

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


  reply	other threads:[~2020-08-05 15:26 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-27 15:51 [dpdk-dev] [PATCH v2] doc/mlx5: add timestamp upper limitation description Viacheslav Ovsiienko
2020-08-05 15:26 ` Thomas Monjalon [this message]
2020-08-05 15:43   ` [dpdk-dev] [PATCH v3] doc: add timestamp upper limitation in mlx5 guide Thomas Monjalon

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