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Date:   Tue, 26 Apr 2022 11:57:52 +0200
From:   Robert Richter <rrichter@amd.com>
To:     Ravi Bangoria <ravi.bangoria@amd.com>
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Subject: Re: [PATCH 2/6] perf/amd/ibs: Advertise zen4_ibs_extensions as pmu
 capability attribute
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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@amd.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.

>  
>  	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;

>  
>  	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.

>  	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.

>  
>  	/*
>  	 * Some chips fail to reset the fetch count when it is written; instead
> @@ -773,6 +792,7 @@ static __init void perf_ibs_fetch_prepare(void)
>  	if (ibs_caps & IBS_CAPS_ZEN4IBSEXTENSIONS) {
>  		perf_ibs_fetch.config_mask |= IBS_FETCH_L3MISSONLY;
>  		*format_attrs++ = &fetch_l3missonly.attr.attr;
> +		*caps_attr++ = &zen4_ibs_extensions.attr.attr;
>  	}
>  
>  	perf_ibs_pmu_init(&perf_ibs_fetch, "ibs_fetch");
> @@ -781,6 +801,7 @@ static __init void perf_ibs_fetch_prepare(void)
>  static __init void perf_ibs_op_prepare(void)
>  {
>  	struct attribute **format_attrs = perf_ibs_op.format_attrs;
> +	struct attribute **caps_attr = perf_ibs_op.caps_attrs;
>  
>  	if (ibs_caps & IBS_CAPS_OPCNT) {
>  		perf_ibs_op.config_mask |= IBS_OP_CNT_CTL;
> @@ -796,6 +817,7 @@ static __init void perf_ibs_op_prepare(void)
>  	if (ibs_caps & IBS_CAPS_ZEN4IBSEXTENSIONS) {
>  		perf_ibs_op.config_mask |= IBS_OP_L3MISSONLY;
>  		*format_attrs++ = &op_l3missonly.attr.attr;
> +		*caps_attr++ = &zen4_ibs_extensions.attr.attr;
>  	}

Also add a termination for caps here.

-Robert

>  
>  	perf_ibs_pmu_init(&perf_ibs_op, "ibs_op");
> -- 
> 2.27.0
>