Re: [PATCH v7 06/10] fs/resctrl: Introduce interface to display "io_alloc" support

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

Hi Reinette,

On 7/21/25 18:36, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/10/25 10:16 AM, Babu Moger wrote:
>> "io_alloc" feature in resctrl allows direct insertion of data from I/O
>> devices into the cache.
>>
>> Introduce the 'io_alloc' resctrl file to indicate the support for the
>> feature.
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
> 
> ...
> 
>> ---
>>  Documentation/filesystems/resctrl.rst | 25 +++++++++++++++++
>>  fs/resctrl/rdtgroup.c                 | 39 +++++++++++++++++++++++++++
>>  2 files changed, 64 insertions(+)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index c3c412733632..354e6a00fa45 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -143,6 +143,31 @@ related to allocation:
>>  			"1":
>>  			      Non-contiguous 1s value in CBM is supported.
>>  
>> +"io_alloc":
>> +		"io_alloc" enables system software to configure the portion of
>> +		the cache allocated for I/O traffic. File may only exist if the
>> +		system supports this feature on some of its cache resources.
>> +
>> +			"disabled":
>> +			      Portions of cache used for allocation of I/O traffic
>> +			      cannot be configured.
>> +			"enabled":
>> +			      Portions of cache used for allocation of I/O traffic
>> +			      can be configured using "io_alloc_cbm".
>> +			"not supported":
>> +			      Support not available on the system.
> 
> "Support not available on the system." -> "Support not available for this resource."?

Sure.

> 
>> +
>> +		The underlying implementation may reduce resources available to
>> +		general (CPU) cache allocation. See architecture specific notes
>> +		below. Depending on usage requirements the feature can be enabled
>> +		or disabled:
> 
> "disabled:" -> "disabled."?

Sure.

> 
>> +
>> +		On AMD systems, the io_alloc feature is supported by the L3 Smart
>> +		Data Cache Injection Allocation Enforcement (SDCIAE). The CLOSID for
>> +		io_alloc is determined by the highest CLOSID supported by the resource.
> 
> "is determined by the" -> "is the"?
> 

Sure.

> To make clear connection with previous paragraph you can append something like:
> 	When io_alloc is enabled on an AMD system the highest CLOSID is dedicated to
> 	io_alloc and no longer available for general (CPU) cache allocation.

Sure.

> 
>> +		When CDP is enabled, io_alloc routes I/O traffic using the highest
>> +		CLOSID allocated for the instruction cache (L3CODE).
> 
> To clear up what happens with L3DATA, what do you think of appending something like:
> 		, making this CLOSID no longer available for general (CPU) cache
> 		allocation for both the L3CODE and L3DATA resources.
> 

Sure.

>> +
>>  Memory bandwidth(MB) subdirectory contains the following files
>>  with respect to allocation:
>>  
>> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
>> index a2eea85aecc8..d7c4417b4516 100644
>> --- a/fs/resctrl/rdtgroup.c
>> +++ b/fs/resctrl/rdtgroup.c
>> @@ -1836,6 +1836,28 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
>>  	return ret ?: nbytes;
>>  }
>>  
>> +static int resctrl_io_alloc_show(struct kernfs_open_file *of,
> 
> Please move to ctrlmondata.c

Yes.

> 
> 
>> +				 struct seq_file *seq, void *v)
>> +{
>> +	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
>> +	struct rdt_resource *r = s->res;
>> +
>> +	mutex_lock(&rdtgroup_mutex);
>> +
>> +	if (r->cache.io_alloc_capable) {
>> +		if (resctrl_arch_get_io_alloc_enabled(r))
>> +			seq_puts(seq, "enabled\n");
>> +		else
>> +			seq_puts(seq, "disabled\n");
>> +	} else {
>> +		seq_puts(seq, "not supported\n");
>> +	}
>> +
>> +	mutex_unlock(&rdtgroup_mutex);
>> +
>> +	return 0;
>> +}
>> +
>>  /* rdtgroup information files for one cache resource. */
>>  static struct rftype res_common_files[] = {
>>  	{
>> @@ -1926,6 +1948,12 @@ static struct rftype res_common_files[] = {
>>  		.kf_ops		= &rdtgroup_kf_single_ops,
>>  		.seq_show	= rdt_thread_throttle_mode_show,
>>  	},
>> +	{
>> +		.name		= "io_alloc",
>> +		.mode		= 0444,
>> +		.kf_ops		= &rdtgroup_kf_single_ops,
>> +		.seq_show	= resctrl_io_alloc_show,
>> +	},
>>  	{
>>  		.name		= "max_threshold_occupancy",
>>  		.mode		= 0644,
>> @@ -2095,6 +2123,15 @@ static void thread_throttle_mode_init(void)
>>  				 RFTYPE_CTRL_INFO | RFTYPE_RES_MB);
>>  }
>>  
>> +static void io_alloc_init(void)
> 
> This function's comment can benefit from a snippet that highlights that
> even though this operates on hardcoded L3 resource it results in this file
> being visible for *all* cache resources (eg. L2 cache also), whether they
> support io_alloc or not.

Added the comment.

> 
>> +{
>> +	struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
>> +
>> +	if (r->cache.io_alloc_capable)
>> +		resctrl_file_fflags_init("io_alloc", RFTYPE_CTRL_INFO |
>> +					 RFTYPE_RES_CACHE);
>> +}
>> +
>>  void resctrl_file_fflags_init(const char *config, unsigned long fflags)
>>  {
>>  	struct rftype *rft;
>> @@ -4282,6 +4319,8 @@ int resctrl_init(void)
>>  
>>  	thread_throttle_mode_init();
>>  
>> +	io_alloc_init();
>> +
>>  	ret = resctrl_mon_resource_init();
>>  	if (ret)
>>  		return ret;
> 
> Reinette
> 

-- 
Thanks
Babu Moger