Date:   Tue, 26 Apr 2022 17:10:51 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Robert Richter <rrichter@....com>
Cc:     peterz@...radead.org, acme@...nel.org, mingo@...hat.com,
        mark.rutland@....com, jolsa@...nel.org, namhyung@...nel.org,
        tglx@...utronix.de, bp@...en8.de, irogers@...gle.com,
        yao.jin@...ux.intel.com, james.clark@....com, leo.yan@...aro.org,
        kan.liang@...ux.intel.com, ak@...ux.intel.com, eranian@...gle.com,
        like.xu.linux@...il.com, x86@...nel.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        sandipan.das@....com, ananth.narayan@....com, kim.phillips@....com,
        santosh.shukla@....com, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH 2/6] perf/amd/ibs: Advertise zen4_ibs_extensions as pmu
 capability attribute



On 26-Apr-22 3:27 PM, Robert Richter wrote:
> On 25.04.22 10:13:19, Ravi Bangoria wrote:
>> PMU driver can advertise certain feature via capability attribute('caps'
>> sysfs directory) which can be consumed by userspace tools like perf. Add
>> zen4_ibs_extensions capability attribute for IBS pmus. This attribute
>> will be enabled when CPUID_Fn8000001B_EAX[11] is set.
>>
>> Without patch:
>>
>>   $ ls /sys/bus/event_source/devices/ibs_op/caps
>>   ls: cannot access '/sys/.../ibs_op/caps': No such file or directory
>>
>> With patch:
>>
>>   $ ls /sys/bus/event_source/devices/ibs_op/caps
>>   zen4_ibs_extensions
>>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
>> ---
>>  arch/x86/events/amd/ibs.c | 34 ++++++++++++++++++++++++++++------
>>  1 file changed, 28 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
>> index a5303d62060c..54e12bd7843e 100644
>> --- a/arch/x86/events/amd/ibs.c
>> +++ b/arch/x86/events/amd/ibs.c
>> @@ -95,8 +95,10 @@ struct perf_ibs {
>>  	struct cpu_perf_ibs __percpu	*pcpu;
>>  
>>  	struct attribute		**format_attrs;
>> +	struct attribute		**caps_attrs;
>>  	struct attribute_group		format_group;
>> -	const struct attribute_group	*attr_groups[2];
>> +	struct attribute_group		caps_group;
>> +	const struct attribute_group	*attr_groups[3];
> 
> Also add a macro for max groups.

Same as previous patch, except defining size of the array, it won't
be used anywhere else.

> 
>>  
>>  	u64				(*get_count)(u64 config);
>>  };
>> @@ -522,10 +524,13 @@ PMU_FORMAT_ATTR(rand_en,	"config:57");
>>  PMU_FORMAT_ATTR(cnt_ctl,	"config:19");
>>  PMU_EVENT_ATTR_STRING(l3missonly, fetch_l3missonly, "config:59");
>>  PMU_EVENT_ATTR_STRING(l3missonly, op_l3missonly, "config:16");
>> +PMU_EVENT_ATTR_STRING(zen4_ibs_extensions, zen4_ibs_extensions, "1");
>>  
>>  /* size = nr attrs plus NULL at the end */
>>  static struct attribute *ibs_fetch_format_attrs[3];
>>  static struct attribute *ibs_op_format_attrs[3];
>> +static struct attribute *ibs_fetch_caps_attrs[2];
>> +static struct attribute *ibs_op_caps_attrs[2];
>>  
>>  static struct perf_ibs perf_ibs_fetch = {
>>  	.pmu = {
>> @@ -548,6 +553,7 @@ static struct perf_ibs perf_ibs_fetch = {
>>  	.offset_mask		= { MSR_AMD64_IBSFETCH_REG_MASK },
>>  	.offset_max		= MSR_AMD64_IBSFETCH_REG_COUNT,
>>  	.format_attrs		= ibs_fetch_format_attrs,
>> +	.caps_attrs		= ibs_fetch_caps_attrs,
>>  
>>  	.get_count		= get_ibs_fetch_count,
>>  };
>> @@ -574,6 +580,7 @@ static struct perf_ibs perf_ibs_op = {
>>  	.offset_mask		= { MSR_AMD64_IBSOP_REG_MASK },
>>  	.offset_max		= MSR_AMD64_IBSOP_REG_COUNT,
>>  	.format_attrs		= ibs_op_format_attrs,
>> +	.caps_attrs		= ibs_op_caps_attrs,
>>  
>>  	.get_count		= get_ibs_op_count,
>>  };
>> @@ -728,6 +735,7 @@ static __init int perf_ibs_pmu_init(struct perf_ibs *perf_ibs, char *name)
>>  {
>>  	struct cpu_perf_ibs __percpu *pcpu;
>>  	int ret;
>> +	int i = 0;
> 
> 'group'? Use a pointer to iterate over groups here same as for attrs?
> 
> 	struct attribute_group **group = &perf_ibs->attr_groups;

Sure.

> 
>>  
>>  	pcpu = alloc_percpu(struct cpu_perf_ibs);
>>  	if (!pcpu)
>> @@ -736,16 +744,26 @@ static __init int perf_ibs_pmu_init(struct perf_ibs *perf_ibs, char *name)
>>  	perf_ibs->pcpu = pcpu;
>>  
>>  	/* register attributes */
>> +	memset(&perf_ibs->attr_groups, 0, sizeof(perf_ibs->attr_groups));
> 
> With a termination below this could be dropped.

I think we can just remove this line. perf_ibs points to either perf_ibs_fetch
or perf_ibs_op, both of which are global variables and would be preinitialized
with 0s.

> 
>>  	if (perf_ibs->format_attrs[0]) {
>>  		memset(&perf_ibs->format_group, 0, sizeof(perf_ibs->format_group));
>> -		perf_ibs->format_group.name	= "format";
>> -		perf_ibs->format_group.attrs	= perf_ibs->format_attrs;
>> +		perf_ibs->format_group.name = "format";
>> +		perf_ibs->format_group.attrs = perf_ibs->format_attrs;
>>  
>> -		memset(&perf_ibs->attr_groups, 0, sizeof(perf_ibs->attr_groups));
>> -		perf_ibs->attr_groups[0]	= &perf_ibs->format_group;
>> -		perf_ibs->pmu.attr_groups	= perf_ibs->attr_groups;
>> +		perf_ibs->attr_groups[i++] = &perf_ibs->format_group;
> 
> So this could be:
> 
> 		*groups++ = &perf_ibs->format_group
> 
>>  	}
>>  
>> +	if (perf_ibs->caps_attrs[0]) {
>> +		memset(&perf_ibs->caps_group, 0, sizeof(perf_ibs->caps_group));
>> +		perf_ibs->caps_group.name = "caps";
>> +		perf_ibs->caps_group.attrs = perf_ibs->caps_attrs;
>> +
>> +		perf_ibs->attr_groups[i++] = &perf_ibs->caps_group;
> 
> Similar here.
> 
>> +	}
> 
> Add a terminating NULL pointer for groups here.
> 
>> +
>> +	if (i)
> 
> 	if (perf_ibs->attr_groups[0])
> 		...
> 
>> +		perf_ibs->pmu.attr_groups = perf_ibs->attr_groups;
>> +
>>  	ret = perf_pmu_register(&perf_ibs->pmu, name, -1);
>>  	if (ret) {
>>  		perf_ibs->pcpu = NULL;
>> @@ -758,6 +776,7 @@ static __init int perf_ibs_pmu_init(struct perf_ibs *perf_ibs, char *name)
>>  static __init void perf_ibs_fetch_prepare(void)
>>  {
>>  	struct attribute **format_attrs = perf_ibs_fetch.format_attrs;
>> +	struct attribute **caps_attr = perf_ibs_fetch.caps_attrs;
> 
> Now I see why it was renamed, ok.

Yup.

Thanks for the review,
Ravi

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