Re: [RFC PATCH v3 17/17] x86/resctrl: Introduce interface to modify assignment states of the groups

Dave Martin
2024-05-02T16:21:33Z

On Thu, Mar 28, 2024 at 08:06:50PM -0500, Babu Moger wrote:
> Introduce rdtgroup_mbm_assign_control_write to assign mbm events.
> Assignment state can be updated by writing to this interface.
> Assignment states are applied on all the domains. Assignment on one
> domain applied on all the domains. User can pass one valid domain and
> assignment will be updated on all the available domains.
>
> Format is similar to the list format with addition of op-code for the
> assignment operation.
>
> * Default CTRL_MON group:
> "//<domain_id><op-code><assignment_flags>"
>
> * Non-default CTRL_MON group:
> "<CTRL_MON group>//<domain_id><op-code><assignment_flags>"
>
> * Child MON group of default CTRL_MON group:
> "/<MON group>/<domain_id><op-code><assignment_flags>"
>
> * Child MON group of non-default CTRL_MON group:
> "<CTRL_MON group>/<MON group>/<domain_id><op-code><assignment_flags>"
>
> Op-code can be one of the following:
>
> = Update the assignment to match the flags
> + Assign a new state
> - Unassign a new state
> _ Unassign all the states
>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
>
> v3: New patch.
> Addresses the feedback to provide the global assignment interface.
> https://lore.kernel.org/lkml/c73f444b-83a1-4e9a-95d3-54c5165ee782@intel.com/
> ---
> Documentation/arch/x86/resctrl.rst | 71 ++++++++
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 236 ++++++++++++++++++++++++-
> 2 files changed, 306 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index 2d96565501ab..64ec70637c66 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -328,6 +328,77 @@ with the following files:
> None of events are assigned on this mon group. This is a child
> monitor group of the non default control mon group.
>
> + Assignment state can be updated by writing to this interface.
> +
> + NOTE: Assignment on one domain applied on all the domains. User can
> + pass one valid domain and assignment will be updated on all the
> + available domains.
> +
> + Format is similar to the list format with addition of op-code for the
> + assignment operation.
> +
> + * Default CTRL_MON group:
> + "//<domain_id><op-code><assignment_flags>"
> +
> + * Non-default CTRL_MON group:
> + "<CTRL_MON group>//<domain_id><op-code><assignment_flags>"
> +
> + * Child MON group of default CTRL_MON group:
> + "/<MON group>/<domain_id><op-code><assignment_flags>"
> +
> + * Child MON group of non-default CTRL_MON group:
> + "<CTRL_MON group>/<MON group>/<domain_id><op-code><assignment_flags>"

The final bullet seems to cover everything, if we allow <CTRL_MON group>
and <MON group> to be independently empty strings to indicate the
default control and/or monitoring group respectively.

Would that be simpler than treating this as four separate cases?

Also, will this go wrong if someone creates a resctrl group with '\n'
(i.e., a newline character) in the name?

> +
> + Op-code can be one of the following:
> + ::
> +
> + = Update the assignment to match the flags
> + + Assign a new state
> + - Unassign a new state
> + _ Unassign all the states

I can't remember whether I already asked this, but is "_" really
needed here?

Wouldn't it be the case that

//*_

would mean just the same thing as

//*=_

...? (assuming the "*" = "all domains" convention already discussed)

Maybe I'm missing something here.

[...]

Cheers
---Dave