From 1a3709c1f021afbe58db4a27a179127e561fe401 Mon Sep 17 00:00:00 2001 From: Viacheslav Ovsiienko Date: Mon, 8 Nov 2021 18:41:01 +0200 Subject: [PATCH] doc: describe timestamp limitations for mlx5 The ConnectX NIC series hardware provides only 63-bit wide timestamps. The imposed limitations description added to documentation. At the moment there are no affected applications known or bug reports neither, this is just the declaration of limitation. Cc: stable@dpdk.org Signed-off-by: Viacheslav Ovsiienko --- doc/guides/nics/mlx5.rst | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst index d175c2061e..552e06c0db 100644 --- a/doc/guides/nics/mlx5.rst +++ b/doc/guides/nics/mlx5.rst @@ -480,6 +480,20 @@ Limitations - Needs OFED 5.4+. +- Timestamps: + + - CQE timestamp field width is limited by hardware to 63 bits, MSB is zero. + - In the free-running mode the timestamp counter is reset on power on + and 63-bit value provides over 1800 years of uptime till overflow. + - In the real-time mode + (configurable with ``REAL_TIME_CLOCK_ENABLE`` firmware settings), + the timestamp presents the nanoseconds elapsed since 01-Jan-1970, + hardware timestamp overflow will happen on 19-Jan-2038 + (0x80000000 seconds since 01-Jan-1970). + - The send scheduling is based on timestamps + from the reference "Clock Queue" completions, + the scheduled send timestamps should not be specified with non-zero MSB. + Statistics ---------- @@ -1242,6 +1256,10 @@ Below are some firmware configurations listed. FLEX_PARSER_PROFILE_ENABLE=4 PROG_PARSE_GRAPH=1 +- enable realtime timestamp format:: + + REAL_TIME_CLOCK_ENABLE=1 + Linux Prerequisites ------------------- -- 2.20.1