RE: [PATCH] net/mlx5: fix read device clock in real time mode

[Raslan Darawsheh <rasland@nvidia.com>]

Hi,

> -----Original Message-----
> From: Slava Ovsiienko <viacheslavo@nvidia.com>
> Sent: Tuesday, January 3, 2023 1:12 PM
> To: dev@dpdk.org
> Cc: Matan Azrad <matan@nvidia.com>; Raslan Darawsheh
> <rasland@nvidia.com>; Ori Kam <orika@nvidia.com>; stable@dpdk.org
> Subject: [PATCH] net/mlx5: fix read device clock in real time mode
> 
> Since ConnectX-6DX the real time timestamp mode is supported.
> The rte_eth_read_clock() routine queries current timestamp value from the
> PMD.
> 
> The mlx5 PMD has special infrastructure to schedule packet sending in real
> time mode which can be engaged with tx_pp devarg.
> This infrastructure provides the timestamp reading from the special queue
> CEQs directly from the host memory in user space, without involving kernel
> calls.
> 
> The ConnectX-7 NIC has hardware capability to schedule packet sending
> without special infrastructure and tx_pp devarg can be omitted. If there is no
> tx_pp devarg specified the mlx5 uses kernel calls to query current timestamp
> value. The kernel can be completely unaware about engaged real time
> mode, also kernel might use its internal queue CQEs to get timestamps, that
> is neither precise nor reliable, inconsistent values might be returned, causing
> send scheduling malfunction.
> 
> The HCA PCI BAR provides the real time direct reading from hardware.
> This patch maps PCI resource to the process address space on demand and
> allows reading the real time timestamp values from the NIC directly.
> 
> Fixes: b94d93ca73803 ("net/mlx5: support reading device clock")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>

Patch applied to next-net-mlx,

Kindest regards,
Raslan Darawsheh