Re: [RFC PATCH v3 05/17] x86/resctrl: Introduce the interface to display the assignment state

Reinette Chatre
2024-05-03T23:28:34Z

Hi Babu,

On 3/28/2024 6:06 PM, Babu Moger wrote:
> The ABMC feature provides an option to the user to assign an RMID
> to the hardware counter and monitor the bandwidth for a longer duration.
> System can be in only one mode at a time (Legacy Monitor mode or ABMC
> mode). By default, ABMC mode is disabled.

"By default, ABMC mode is disabled." seems to contradict later work.

>
> Provide an interface to display the monitor mode on the system.
> $cat /sys/fs/resctrl/info/L3_MON/mbm_assign
> abmc

This example seems to contradict earlier statements in two ways:
(a) it only shows one mode vs. there are two modes (legacy or ABMC)
(b) there is no active mode vs. one mode is always active.

>
> When the feature is enabled
> $cat /sys/fs/resctrl/info/L3_MON/mbm_assign
> [abmc]
>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
> v3: New patch to display ABMC capability.
> ---
> Documentation/arch/x86/resctrl.rst | 5 +++++
> arch/x86/kernel/cpu/resctrl/monitor.c | 4 +++-
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 17 +++++++++++++++++
> 3 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index 68df7751d1f5..cd973a013525 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -257,6 +257,11 @@ with the following files:
> # cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config
> 0=0x30;1=0x30;3=0x15;4=0x15
>
> +"mbm_assign":
> + Available when assignable monitoring features are supported.
> + Reports the list of assignable features supported and the enclosed brackets
> + indicate the feature is enabled.

"indicate the feature is enabled" -> "indicate which feature is enabled" or
"indicates the currently enabled feature" or ...?

> +
> "max_threshold_occupancy":
> Read/write file provides the largest value (in
> bytes) at which a previously used LLC_occupancy
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 735b449039c1..48d1957ea5a3 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -1058,8 +1058,10 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
> RFTYPE_MON_INFO | RFTYPE_RES_CACHE);
> }
>
> - if (resctrl_arch_has_abmc(r))
> + if (resctrl_arch_has_abmc(r)) {
> r->mbm_assign_capable = ABMC_ASSIGN;
> + resctrl_file_fflags_init("mbm_assign", RFTYPE_MON_INFO);

I think this will need some more thought when considering the fs/arch split.
The architecture can be expected to set r->mbm_assign_capable as above but
having the architecture meddle with the fs flags does not seem like the right
thing to do. I think that RFTYPE_MON_INFO may not be accessible to arch code
anyway.

> + }
> }
>
> l3_mon_evt_init(r);
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index dda71fb6c10e..5ec807e8dd38 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -846,6 +846,17 @@ static int rdtgroup_rmid_show(struct kernfs_open_file *of,
> return ret;
> }
>
> +static int rdtgroup_mbm_assign_show(struct kernfs_open_file *of,
> + struct seq_file *s, void *v)
> +{
> + struct rdt_resource *r = of->kn->parent->priv;
> +
> + if (r->mbm_assign_capable)
> + seq_puts(s, "abmc\n");
> +
> + return 0;
> +}

Should it print "legacy" if not mbm_assign_capable? Or actually, I think
the expectation is that this file will only be accessible if
r->mbm_assign_capable is true ... so having that if (r->mbm_assign_capable)
check is not clear to me ... if that is false then it would be a kernel
bug, no?

> +
> #ifdef CONFIG_PROC_CPU_RESCTRL
>
> /*
> @@ -1903,6 +1914,12 @@ static struct rftype res_common_files[] = {
> .seq_show = mbm_local_bytes_config_show,
> .write = mbm_local_bytes_config_write,
> },
> + {
> + .name = "mbm_assign",
> + .mode = 0444,
> + .kf_ops = &rdtgroup_kf_single_ops,
> + .seq_show = rdtgroup_mbm_assign_show,
> + },
> {
> .name = "cpus",
> .mode = 0644,

Reinette