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SubjectRe: [PATCH v3 15/21] x86/resctrl: Abstract __rmid_read()
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Hi Reinette,

On 16/03/2022 21:52, Reinette Chatre wrote:
> On 2/17/2022 10:21 AM, James Morse wrote:
>> __rmid_read() selects the specified eventid and returns the counter
>> value from the MSR. The error handling is architecture specific, and
>> handled by the callers, rdtgroup_mondata_show() and __mon_event_count().
>>
>> Error handling should be handled by architecture specific code, as
>> a different architecture may have different requirements. MPAM's
>> counters can report that they are 'not ready', requiring a second
>> read after a short delay. This should be hidden from resctrl.
>>
>> Make __rmid_read() the architecture specific function for reading
>> a counter. Rename it resctrl_arch_rmid_read() and move the error
>> handling into it.

>> @@ -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;
>> }
>
> From above we see that resctrl_arch_rmid_read() returns an int that could be
> -EIO or -EINVAL ...
>
> ...
>
>> @@ -319,15 +331,15 @@ static u64 __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;
>> +
>
> Setting rr->err, an int, to the return of resctrl_arch_rmid_read() is ok and
> can handle the negative error codes, but returning it here means that
> __mon_event_count()'s return type should be changed,
> it is currently u64.

Good point. Fixed.


>> @@ -419,9 +431,14 @@ void mon_event_count(void *info)
>> }
>> }
>>
>
> Also take care here ... ret_val in mon_event_count() is still u64 while
> __mon_event_count() attempts to return negative errors.

(yup, fixed)


>> - /* 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.
>> + * If the first call for the control group succeed, discard any error
>> + * set by reads of monitor groups.
>> + */
>
> Additionally, if the first call fails, but a following read of monitor group
> succeeds then the first call's error is discarded.
>
> How about if the last sentence is replaced with:
> "Discard error if any of the monitor event reads succeeded."

Sure,


Thanks,

James

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