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

Moger, Babu
2024-05-07T16:28:28Z

Hi Reinette,

On 5/3/24 18:28, Reinette Chatre wrote:
> 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.

Yes. Will correct it.

>
>>
>> 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.

I need to correct the commit messages. At this point this interface is
read-only. I will move some of this commit message to patch 15/17.

>
>>
>> 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 ...?

This looks good.

>
>> +
>> "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.

It is accessible to both arch and fs code per latest code.
https://lore.kernel.org/lkml/20240426150904.8854-33-Dave.Martin@arm.com/

>
>> + }
>> }
>>
>> 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)

Correct. I need to move code from patch 7/17 here to correct this.

> check is not clear to me ... if that is false then it would be a kernel
> bug, no?

Yes. This is not correct. I need to fix this.

>
>> +
>> #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
>

--
Thanks
Babu Moger