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

[Moger, Babu]

Hi Reinette,

On 3/21/25 18:00, Reinette Chatre wrote:
> 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).

Yes. Will remove "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()?

parse_cbm() needs rdtgrp to read 'mode' and 'closid' which is passed in
rdt_parse_data.


We can call parse_cbm directly if we add 'mode' and closid in
rdt_parse_data.  Will add those changes in next revision.


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

Sure. Will do.

> 
> Reinette
> 

-- 
Thanks
Babu Moger