Re: [PATCH v7 20/24] x86/resctrl: Introduce the interface to switch between monitor modes

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

Hi Reinette,

On 9/19/24 12:38, Reinette Chatre wrote:
> Hi Babu,
> 
> On 9/4/24 3:21 PM, 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>
>> ---
>> v7: Changed the interface name to mbm_assign_mode.
>>     Removed the references of ABMC.
>>     Added the changes to reset global and domain bitmaps.
>>     Added the changes to reset rmid.
>>
>> v6: Changed the mode name to mbm_cntr_assign.
>>     Moved all the FS related code here.
>>     Added changes to reset mbm_cntr_map and resctrl group counters.
>> ""
>> v5: Change log and mode description text correction.
>>
>> v4: Minor commit text changes. Keep the default to ABMC when supported.
>>     Fixed comments to reflect changed interface "mbm_mode".
>>
>> v3: New patch to address the review comments from upstream.
>> ---
>>  Documentation/arch/x86/resctrl.rst     | 15 ++++++
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 74 +++++++++++++++++++++++++-
>>  2 files changed, 88 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index ff5397d19704..743c0b64a330 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -290,6 +290,21 @@ with the following files:
>>  	than 'num_mbm_cntrs' to be created. Reading the mbm files may report 'Unavailable'
>>  	if there is no hardware resource assigned.
>>  
>> +	* To enable ABMC feature:
> 
> The separation between fs and arch did not make it to this patch?

My bad. Will change the text.

> 
>> +	  ::
>> +
>> +	    # echo  "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>> +	* To enable the legacy monitoring feature:
> 
> "legacy" -> "default"?

Sure.

> 
>> +	  ::
>> +
>> +	    # echo  "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>> +	The MBM event counters will reset when mbm_assign_mode is changed. Moving to
> 
> "will reset" -> "may reset"? Please also be clear on what is meant with "MBM event counter".

It "will reset".

> Note that "counter" has a very specific meaning in this work and after considering that
> it is not clear if "MBM event counter will reset" means that the counters are no longer
> assigned or if it means that the counts associated with events will be reset.

How about

"The MBM event counters(mbm_total_bytes and mbm_local_bytes) associated
with the event will reset when mbm_assign_mode is changed."

> 
>> +	mbm_cntr_assign will require users to assign the counters to the events to
>> +	read the events. Otherwise, the MBM event counters will return "Unassigned"
>> +	when read.
>> +
>>  "num_mbm_cntrs":
>>  	The number of monitoring counters available for assignment.
>>  
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index bf94e4e05540..7a8ece12d7da 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -895,6 +895,77 @@ static int rdtgroup_mbm_assign_mode_show(struct kernfs_open_file *of,
>>  	return 0;
>>  }
>>  
>> +static void rdtgroup_mbm_cntr_reset(struct rdt_resource *r)
> 
> It is not clear why this has "rdtgroup" prefix since it is not specific to
> a resource group but a global action that resets all counters.

Sure. Will remote prefix.

> 
>> +{
>> +	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;
>> +		}
>> +	}
>> +}
>> +
>> +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;
>> +	}
>> +
>> +	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
>> +		rdtgroup_mbm_cntr_reset(r);
> 
> Should this reset not happen only after the hardware state was changed
> successfully? If the arch change failed then this may lead to inconsistent
> state.

Sure. Will move after the mode is changed.

> 
>> +		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
>> +	}
>> +
>> +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)
>>  {
>> @@ -2107,9 +2178,10 @@ 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
> 

-- 
Thanks
Babu Moger