[PATCH v1] doc/guides: update monitor PMD mode description

[Bruce Richardson]

On Fri, Feb 21, 2025 at 04:54:40PM +0000, Chris MacNamara wrote:
> A recent CPU change requires an extra enabling step for
> the umonitor instruction on Intel CPUs.
> This is now detailed in the l3 fwd power manager doc.
> 
> Signed-off-by: Chris MacNamara <chris.macnamara at intel.com>
> ---
>  .mailmap                                          | 1 +
>  doc/guides/sample_app_ug/l3_forward_power_man.rst | 5 +++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/.mailmap b/.mailmap
> index a03d3cfb59..c4bc38752f 100644
> --- a/.mailmap
> +++ b/.mailmap
> @@ -263,6 +263,7 @@ Christopher Reder <christopher.reder at broadcom.com>
>  Christoph Gysin <christoph.gysin at gmail.com>
>  Christos Ricudis <ricudis at niometrics.com>
>  Chris Wright <chrisw at redhat.com>
> +Chris MacNamara <chris.macnamara at intel.com>

Minor nit, this is kept in alphabetical order, so your name should go just
above Chris Wright's one.

>  Chuanshe Zhang <zhangchuanshe at icloudshield.com>
>  Chuanyu Xue <chuanyu.xue at uconn.edu>
>  Chuhong Yao <ych at panath.cn>
> diff --git a/doc/guides/sample_app_ug/l3_forward_power_man.rst b/doc/guides/sample_app_ug/l3_forward_power_man.rst
> index 3271bc2154..d0af28e0ec 100644
> --- a/doc/guides/sample_app_ug/l3_forward_power_man.rst
> +++ b/doc/guides/sample_app_ug/l3_forward_power_man.rst
> @@ -293,6 +293,11 @@ and has three available power management schemes:
>  ``monitor``
>    This will use ``rte_power_monitor()`` function to enter
>    a power-optimized state (subject to platform support).
> +  On recent Gen 4 Xeon Scalable Processors the umonitor instruction
> +  is disabled by default.
> +  An additional step is required to enable the umonitor instruction.
> +  Writing 0 to bit 6 of register 0x123 will enable umonitor.
> +  `More details are available via Monitor and Umonitor Performance Guidance <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/monitor-umonitor-performance-guidance.html>`_
>  
>  ``pause``
>    This will use ``rte_power_pause()`` or ``rte_pause()``
> -- 

I'd suggest this extra info be added as a note, rather than inline in the
text, since it's not applicable to all systems. I'd also suggest that an
equivalent note needs to be added to the programmer's guide doc, in [1].
The info is relevant for those using the library, as well as those just
using the sample app.

/Bruce

[1] https://doc.dpdk.org/guides/prog_guide/power_man.html#ethernet-pmd-power-management-api