Re: [PATCH v11 10/23] x86/resctrl: Remove MSR reading of event configuration value

[Reinette Chatre]

Hi Babu,

On 1/22/25 12:20 PM, Babu Moger wrote:
> The event configuration is domain specific and initialized during domain
> initialization. The values are stored in struct rdt_hw_mon_domain.
> 
> It is not required to read the configuration register every time user asks
> for it. Use the value stored in struct rdt_hw_mon_domain instead.
> 
> Introduce resctrl_arch_mon_event_config_get() and
> resctrl_arch_mon_event_config_set() to get/set architecture domain specific
> mbm_total_cfg/mbm_local_cfg values.
> 
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> ---

> ---
>  arch/x86/kernel/cpu/resctrl/internal.h | 15 +++++++
>  arch/x86/kernel/cpu/resctrl/monitor.c  | 46 +++++++++++++++++++
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 61 +++++---------------------
>  3 files changed, 72 insertions(+), 50 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index ab28b9340ee7..cfaea20145d0 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -605,6 +605,18 @@ union cpuid_0x10_x_edx {
>  	unsigned int full;
>  };
>  
> +/**
> + * struct mon_config_info - Monitoring event configuratiin details

Same typo as previous version. 

> + * @d:			Domain for the event
> + * @evtid:		Event type
> + * @mon_config:		Event configuration value
> + */
> +struct mon_config_info {
> +	struct rdt_mon_domain *d;
> +	enum resctrl_event_id evtid;
> +	u32 mon_config;
> +};
> +
>  void rdt_last_cmd_clear(void);
>  void rdt_last_cmd_puts(const char *s);
>  __printf(1, 2)
> @@ -674,4 +686,7 @@ int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable);
>  bool resctrl_arch_mbm_cntr_assign_enabled(struct rdt_resource *r);
>  void arch_mbm_evt_config_init(struct rdt_hw_mon_domain *hw_dom);
>  unsigned int mon_event_config_index_get(u32 evtid);
> +void resctrl_arch_mon_event_config_set(void *info);
> +u32 resctrl_arch_mon_event_config_get(struct rdt_mon_domain *d,
> +				      enum resctrl_event_id eventid);
>  #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 8917c7261680..6fe9e610e9a0 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -1324,3 +1324,49 @@ int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable)
>  
>  	return 0;
>  }
> +
> +u32 resctrl_arch_mon_event_config_get(struct rdt_mon_domain *d,
> +				      enum resctrl_event_id eventid)
> +{
> +	struct rdt_hw_mon_domain *hw_dom = resctrl_to_arch_mon_dom(d);
> +
> +	switch (eventid) {
> +	case QOS_L3_OCCUP_EVENT_ID:
> +		break;
> +	case QOS_L3_MBM_TOTAL_EVENT_ID:
> +		return hw_dom->mbm_total_cfg;
> +	case QOS_L3_MBM_LOCAL_EVENT_ID:
> +		return hw_dom->mbm_local_cfg;
> +	}
> +
> +	/* Never expect to get here */
> +	WARN_ON_ONCE(1);
> +
> +	return INVALID_CONFIG_VALUE;
> +}
> +
> +void resctrl_arch_mon_event_config_set(void *info)
> +{
> +	struct mon_config_info *mon_info = info;
> +	struct rdt_hw_mon_domain *hw_dom;
> +	unsigned int index;
> +
> +	index = mon_event_config_index_get(mon_info->evtid);
> +	if (index == INVALID_CONFIG_INDEX)
> +		return;
> +
> +	wrmsr(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config, 0);
> +
> +	hw_dom = resctrl_to_arch_mon_dom(mon_info->d);
> +
> +	switch (mon_info->evtid) {
> +	case QOS_L3_MBM_TOTAL_EVENT_ID:
> +		hw_dom->mbm_total_cfg = mon_info->mon_config;
> +		break;
> +	case QOS_L3_MBM_LOCAL_EVENT_ID:
> +		hw_dom->mbm_local_cfg = mon_info->mon_config;
> +		break;
> +	default:
> +		break;
> +	}
> +}

This new arch API has sharp corners because of asymmetry of where resctrl
runs the arch function. I do not think it is required to change this since we
can only speculate about how this may be used in the future but I do think
it will be helpful to add comments that highlight:

resctrl_arch_mon_event_config_get() ->  May run on CPU that does not belong to domain.
resctrl_arch_mon_event_config_set() ->  Runs on CPU that belongs to domain.

... 

> @@ -1683,33 +1653,23 @@ static int mbm_local_bytes_config_show(struct kernfs_open_file *of,
>  	return 0;
>  }
>  
> -static void mon_event_config_write(void *info)
> -{
> -	struct mon_config_info *mon_info = info;
> -	unsigned int index;
> -
> -	index = mon_event_config_index_get(mon_info->evtid);
> -	if (index == INVALID_CONFIG_INDEX) {
> -		pr_warn_once("Invalid event id %d\n", mon_info->evtid);
> -		return;
> -	}
> -	wrmsr(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config, 0);
> -}
>  
>  static void mbm_config_write_domain(struct rdt_resource *r,
>  				    struct rdt_mon_domain *d, u32 evtid, u32 val)
>  {
>  	struct mon_config_info mon_info = {0};

As discussed in previous version it is unnecessary to explicitly initialize
the structure if it is fully initialized in the code. This avoids need for
future cleanups like commit 29eaa7958367 ("x86/resctrl: Slightly clean-up mbm_config_show()")

Reinette