Re: [PATCH v4 15/21] x86/resctrl: Abstract __rmid_read()

[Fenghua Yu]

Hi, James,

On Tue, Apr 12, 2022 at 12:44:13PM +0000, James Morse wrote:
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 71a13c04a846..20c54cbadc0c 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -167,9 +167,9 @@ void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d,
>  		memset(am, 0, sizeof(*am));
>  }
>  
> -static u64 __rmid_read(u32 rmid, enum resctrl_event_id eventid)
> +int resctrl_arch_rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
>  {
> -	u64 val;
> +	u64 msr_val;
>  
>  	/*
>  	 * As per the SDM, when IA32_QM_EVTSEL.EvtID (bits 7:0) is configured
> @@ -180,14 +180,24 @@ static u64 __rmid_read(u32 rmid, enum resctrl_event_id eventid)
>  	 * are error bits.
>  	 */
>  	wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
> -	rdmsrl(MSR_IA32_QM_CTR, val);
> +	rdmsrl(MSR_IA32_QM_CTR, msr_val);
>  
> -	return val;
> +	if (msr_val & RMID_VAL_ERROR)
> +		return -EIO;
> +	if (msr_val & RMID_VAL_UNAVAIL)
> +		return -EINVAL;
> +
> +	*val = msr_val;
> +
> +	return 0;
>  }
>  
>  static bool rmid_dirty(struct rmid_entry *entry)
>  {
> -	u64 val = __rmid_read(entry->rmid, QOS_L3_OCCUP_EVENT_ID);
> +	u64 val = 0;
> +
> +	if (resctrl_arch_rmid_read(entry->rmid, QOS_L3_OCCUP_EVENT_ID, &val))
> +		return true;
>  
>  	return val >= resctrl_cqm_threshold;
>  }
> @@ -259,8 +269,8 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  {
>  	struct rdt_resource *r;
>  	struct rdt_domain *d;
> -	int cpu;
> -	u64 val;
> +	int cpu, err;
> +	u64 val = 0;
>  
>  	r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>  
> @@ -268,8 +278,10 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  	cpu = get_cpu();
>  	list_for_each_entry(d, &r->domains, list) {
>  		if (cpumask_test_cpu(cpu, &d->cpu_mask)) {
> -			val = __rmid_read(entry->rmid, QOS_L3_OCCUP_EVENT_ID);
> -			if (val <= resctrl_cqm_threshold)
> +			err = resctrl_arch_rmid_read(entry->rmid,
> +						     QOS_L3_OCCUP_EVENT_ID,
> +						     &val);
> +			if (err || val <= resctrl_cqm_threshold)
>  				continue;
>  		}
>  
> @@ -315,19 +327,19 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
>  	return chunks >> shift;
>  }
>  
> -static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
> +static int __mon_event_count(u32 rmid, struct rmid_read *rr)
>  {
>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(rr->r);
>  	struct mbm_state *m;
> -	u64 chunks, tval;
> +	u64 chunks, tval = 0;
>  
>  	if (rr->first)
>  		resctrl_arch_reset_rmid(rr->r, rr->d, rmid, rr->evtid);
>  
> -	tval = __rmid_read(rmid, rr->evtid);
> -	if (tval & (RMID_VAL_ERROR | RMID_VAL_UNAVAIL)) {
> -		return tval;
> -	}
> +	rr->err = resctrl_arch_rmid_read(rmid, rr->evtid, &tval);
> +	if (rr->err)
> +		return rr->err;
> +
>  	switch (rr->evtid) {
>  	case QOS_L3_OCCUP_EVENT_ID:
>  		rr->val += tval;
> @@ -343,7 +355,7 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
>  		 * Code would never reach here because an invalid
>  		 * event id would fail the __rmid_read.
>  		 */
> -		return RMID_VAL_ERROR;
> +		return -EINVAL;
>  	}
>  
>  	if (rr->first) {
> @@ -399,7 +411,7 @@ void mon_event_count(void *info)
>  	struct rdtgroup *rdtgrp, *entry;
>  	struct rmid_read *rr = info;
>  	struct list_head *head;
> -	u64 ret_val;
> +	int ret_val;

Now ret_val's meaning is changed from rmid value to error value.
I would suggest to name it as "ret" to avoid confusion that this is still a
returned rmid value.

>  
>  	rdtgrp = rr->rgrp;
>  
> @@ -419,9 +431,13 @@ void mon_event_count(void *info)
>  		}
>  	}
>  
> -	/* Report error if none of rmid_reads are successful */
> -	if (ret_val)
> -		rr->val = ret_val;
> +	/*
> +	 * __mon_event_count() calls for newly created monitor groups may
> +	 * report -EINVAL/Unavailable if the monitor hasn't seen any traffic.
> +	 * Discard error if any of the monitor event reads succeeded.
> +	 */
> +	if (ret_val == 0)
> +		rr->err = 0;
>  }
>  

Thanks.

-Fenghua