Re: [PATCH v3 7/7] x86/resctrl: Introduce interface to modify io_alloc Capacity Bit Masks

[Reinette Chatre]

Hi Babu,

On 1/30/25 1:20 PM, Babu Moger wrote:
> "io_alloc" feature is a mechanism that enables direct insertion of data
> from I/O devices into the L3 cache. By directly caching data from I/O
> devices rather than first storing the I/O data in DRAM, it reduces the
> demands on DRAM bandwidth and reduces latency to the processor consuming
> the I/O data.
> 
> io_alloc feature uses the highest CLOSID to route the traffic from I/O
> devices. Provide the interface to modify io_alloc CBMs (Capacity Bit Mask)
> when feature is enabled.
> 
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> ---
> v3: Minor changes due to changes in resctrl_arch_get_io_alloc_enabled()
>     and resctrl_io_alloc_closid_get().
>     Taken care of handling the CBM update when CDP is enabled.
>     Updated the commit log to make it generic.
> 
> v2: Added more generic text in documentation.
> ---
>  Documentation/arch/x86/resctrl.rst        |  12 ++
>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c |   2 +-
>  arch/x86/kernel/cpu/resctrl/internal.h    |   1 +
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 134 +++++++++++++++++++++-
>  4 files changed, 147 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index 1b67e31d626c..29c8851bcc7f 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -169,6 +169,18 @@ related to allocation:
>  		When CDP is enabled, io_alloc routes I/O traffic using the highest
>  		CLOSID allocated for the instruction cache.
>  
> +"io_alloc_cbm":
> +		Capacity Bit Masks (CBMs) available to supported IO devices which
> +		can directly insert cache lines in L3 which can help to reduce the
> +		latency. CBM can be configured by writing to the interface in the
> +		following format::
> +
> +			L3:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...

This format is dependent on the resource name (not always L3).

> +
> +		When CDP is enabled, L3 control is divided into two separate resources:
> +		L3CODE and L3DATA. However, the CBM can only be updated on the L3CODE
> +		resource.
> +
>  Memory bandwidth(MB) subdirectory contains the following files
>  with respect to allocation:
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index d272dea43924..4dfee0436c1c 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -102,7 +102,7 @@ int parse_bw(struct rdt_parse_data *data, struct resctrl_schema *s,
>   * requires at least two bits set.
>   * AMD allows non-contiguous bitmasks.
>   */
> -static bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r)
> +bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r)
>  {
>  	unsigned long first_bit, zero_bit, val;
>  	unsigned int cbm_len = r->cache.cbm_len;
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 07cf8409174d..702f6926bbdf 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -669,4 +669,5 @@ void rdt_staged_configs_clear(void);
>  bool closid_allocated(unsigned int closid);
>  int resctrl_find_cleanest_closid(void);
>  void show_doms(struct seq_file *s, struct resctrl_schema *schema, int closid);
> +bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r);
>  #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 81b9d8c5dabf..9997cbfc1c19 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1999,6 +1999,137 @@ static int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of,
>  	return ret;
>  }
>  
> +/*
> + * Read the CBM and check the validity. Make sure CBM is not shared
> + * with any other exclusive resctrl groups.
> + */
> +static int resctrl_io_alloc_parse_cbm(char *buf, struct resctrl_schema *s,
> +				      struct rdt_ctrl_domain *d)
> +{
> +	struct resctrl_staged_config *cfg;
> +	struct rdt_resource *r = s->res;
> +	u32 io_alloc_closid;
> +	u32 cbm_val;
> +
> +	cfg = &d->staged_config[s->conf_type];
> +	if (cfg->have_new_ctrl) {
> +		rdt_last_cmd_printf("Duplicate domain %d\n", d->hdr.id);
> +		return -EINVAL;
> +	}
> +
> +	if (!cbm_validate(buf, &cbm_val, r))
> +		return -EINVAL;
> +
> +	/*
> +	 * The CBM may not overlap with other exclusive group.
> +	 */
> +	io_alloc_closid = resctrl_io_alloc_closid_get(r, s);
> +	if (rdtgroup_cbm_overlaps(s, d, cbm_val, io_alloc_closid, true)) {
> +		rdt_last_cmd_puts("Overlaps with exclusive group\n");
> +		return -EINVAL;
> +	}
> +
> +	cfg->new_ctrl = cbm_val;
> +	cfg->have_new_ctrl = true;
> +
> +	return 0;
> +}

Could you please reduce amount of duplication with parse_cbm()?

(for rest of patch, please check that related comments from previous patches
are addressed here also)

Reinette