Re: [PATCH v8 21/25] x86/resctrl: Introduce the interface to switch between monitor modes

["Moger, Babu" <bmoger@amd.com>]

Hi Reinette,

On 10/15/2024 10:36 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 10/9/24 10:39 AM, Babu Moger wrote:
>> Introduce interface to switch between mbm_cntr_assign and default modes.
>>
>> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> [mbm_cntr_assign]
>> default
>>
>> To enable the "mbm_cntr_assign" mode:
>> $ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> To enable the default monitoring mode:
>> $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> MBM event counters will reset when mbm_assign_mode is changed.
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
> 
> ...
> 
>> ---
>>   Documentation/arch/x86/resctrl.rst     | 15 ++++++
>>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 75 +++++++++++++++++++++++++-
>>   2 files changed, 89 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index 99ee9c87952b..d9574078f735 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -291,6 +291,21 @@ with the following files:
>>   	that case reading the mbm_total_bytes and mbm_local_bytes may report
>>   	'Unavailable' if there is no counter associated with that group.
>>   
>> +	* To enable "mbm_cntr_assign" mode:
>> +	  ::
>> +
>> +	    # echo  "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> 
> extra spaces

Sure.

> 
>> +
>> +	* To enable default monitoring mode:
>> +	  ::
>> +
>> +	    # echo  "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> 
> extra spaces

Sure


>> +
>> +	The MBM events (mbm_total_bytes and/or mbm_local_bytes) associated counters
> 
> I did ask you not to copy the text verbatim
> https://lore.kernel.org/all/b38c93bf-4650-45d1-9aca-8b4c4d425886@intel.com/

Outch Yea.

The MBM events (mbm_total_bytes and/or mbm_local_bytes) associated with
counters may reset when mbm_assign_mode is changed.

> 
>> +	may reset when the mode is changed. Moving to mbm_cntr_assign mode will
>> +	require users to assign the counters to the events. Otherwise, the MBM
> 
> "will require" -> "require"
> 
>> +	event counters will return "Unassigned" when read.
>> +
>>   "num_mbm_cntrs":
>>   	The number of monitoring counters available for assignment when the
>>   	architecture supports mbm_cntr_assign mode.
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index cb2c60c0319e..88eda3cf5c82 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -888,6 +888,78 @@ static int rdtgroup_mbm_assign_mode_show(struct kernfs_open_file *of,
>>   	return 0;
>>   }
>>   
>> +static void mbm_cntr_reset(struct rdt_resource *r)
>> +{
>> +	struct rdtgroup *prgrp, *crgrp;
>> +	struct rdt_mon_domain *dom;
>> +
>> +	/*
>> +	 * Hardware counters will reset after switching the monitor mode.
>> +	 * Reset the architectural state so that reading of hardware
>> +	 * counter is not considered as an overflow in the next update.
>> +	 * Also reset the domain counter bitmap.
>> +	 */
>> +	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
>> +		bitmap_zero(dom->mbm_cntr_map, r->mon.num_mbm_cntrs);
>> +		resctrl_arch_reset_rmid_all(r, dom);
>> +	}
>> +
>> +	/* Reset global MBM counter map */
>> +	bitmap_fill(r->mon.mbm_cntr_free_map, r->mon.num_mbm_cntrs);
>> +
>> +	/* Reset the cntr_id's for all the monitor groups */
>> +	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
>> +		prgrp->mon.cntr_id[0] = MON_CNTR_UNSET;
>> +		prgrp->mon.cntr_id[1] = MON_CNTR_UNSET;
>> +		list_for_each_entry(crgrp, &prgrp->mon.crdtgrp_list,
>> +				    mon.crdtgrp_list) {
>> +			crgrp->mon.cntr_id[0] = MON_CNTR_UNSET;
>> +			crgrp->mon.cntr_id[1] = MON_CNTR_UNSET;
>> +		}
> 
> Please use MBM_EVENT_ARRAY_INDEX

Sure.

> 
>> +	}
>> +}
>> +
>> +static ssize_t rdtgroup_mbm_assign_mode_write(struct kernfs_open_file *of,
>> +					      char *buf, size_t nbytes, loff_t off)
>> +{
>> +	struct rdt_resource *r = of->kn->parent->priv;
>> +	int ret = 0;
>> +	bool enable;
>> +
>> +	/* Valid input requires a trailing newline */
>> +	if (nbytes == 0 || buf[nbytes - 1] != '\n')
>> +		return -EINVAL;
>> +
>> +	buf[nbytes - 1] = '\0';
>> +
>> +	cpus_read_lock();
>> +	mutex_lock(&rdtgroup_mutex);
>> +
>> +	rdt_last_cmd_clear();
>> +
>> +	if (!strcmp(buf, "default")) {
>> +		enable = 0;
>> +	} else if (!strcmp(buf, "mbm_cntr_assign")) {
>> +		enable = 1;
>> +	} else {
>> +		ret = -EINVAL;
>> +		rdt_last_cmd_puts("Unsupported assign mode\n");
>> +		goto write_exit;
>> +	}
> 
> Please keep two things in mind:
> * this file is always accessible, whether platform supports assignable
>    counters or not.
> * this is resctrl fs code.
> 
> So, considering above, how should user interpret the "Unsupported assign mode"?
> Shouldn't it also return this error if a user attempts to enable
> "mbm_cntr_assign" on a platform that does not support this mode?
> 
>> +
>> +	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
> 
> resctrl_arch_mbm_cntr_assign_enabled() returns true if mbm_cntr_assign
> mode is enabled, but when it returns false it could mean different things:
> platform supports mbm_cntr_assign mode, but it is disabled, or platform
> does not support mbm_cntr_assign mode.
> 
> resctrl fs should not rely on all archs to duplicate the all the checking done
> in resctrl_arch_mbm_cntr_assign_set(). It should never ask arch to enable a mode
> that it knows the platform is not capable of.

Agree. This should take care of it. Good catch.


  if (!strcmp(buf, "default")) {
             enable = 0;
  } else if (!strcmp(buf, "mbm_cntr_assign")) {
          if (r->mon.mbm_cntr_assignable) {
                  enable = 1;
           } else {
            ret = -EINVAL;
            rdt_last_cmd_puts("mbm_cntr_assign mode is not supported\n");
            goto write_exit;
           }
  } else {
         ret = -EINVAL;
         rdt_last_cmd_puts("Unsupported assign mode\n");
         goto write_exit;
  }


> 
>> +		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
>> +		if (!ret)
>> +			mbm_cntr_reset(r);
>> +	}
>> +
>> +write_exit:
>> +	mutex_unlock(&rdtgroup_mutex);
>> +	cpus_read_unlock();
>> +
>> +	return ret ?: nbytes;
>> +}
>> +
>>   static int rdtgroup_num_mbm_cntrs_show(struct kernfs_open_file *of,
>>   				       struct seq_file *s, void *v)
>>   {
>> @@ -2115,9 +2187,10 @@ static struct rftype res_common_files[] = {
>>   	},
>>   	{
>>   		.name		= "mbm_assign_mode",
>> -		.mode		= 0444,
>> +		.mode		= 0644,
>>   		.kf_ops		= &rdtgroup_kf_single_ops,
>>   		.seq_show	= rdtgroup_mbm_assign_mode_show,
>> +		.write		= rdtgroup_mbm_assign_mode_write,
>>   		.fflags		= RFTYPE_MON_INFO,
>>   	},
>>   	{
> 
> Reinette
> 
> 

-- 
- Babu Moger