Message-ID: <ccff50fc-c802-4352-9859-107138f103c8@intel.com>
Date: Mon, 21 Jul 2025 16:36:49 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>
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Subject: Re: [PATCH v7 06/10] fs/resctrl: Introduce interface to display
 "io_alloc" support

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@....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."?

> +
> +		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."?

> +
> +		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"?

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.

> +		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.

> +
>  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


> +				 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.

> +{
> +	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

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