linux-kernel - Re: [PATCH RFC 1/1] perf stat: do not fatal if the leader is errored

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Date:   Thu, 22 Sep 2022 09:34:17 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Like Xu <like.xu.linux@...il.com>,
        Dongli Zhang <dongli.zhang@...cle.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, joe.jin@...cle.com,
        linux-perf-users@...r.kernel.org, kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH RFC 1/1] perf stat: do not fatal if the leader is errored



On 2022-09-22 4:07 a.m., Like Xu wrote:
> On 22/9/2022 3:10 pm, Dongli Zhang wrote:
>> There are three options to fix the issue.
>>
>> 1. Do not expose /sys/bus/event_source/devices/cpu/events/slots to
>> userspace so that pmu_have_event(pmu->name, "slots") returns false.
> 
> IMO, the guest PMU driver should be fixed
> since it misrepresents emulated hardware capabilities in terms of slots.

Yes, we need to fix the kernel to hide the slots event if it's not
available.

The patch as below should fix it. (Not tested yet)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index b20e646c8205..27ee43faba32 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -5565,6 +5565,19 @@ static struct attribute *intel_pmu_attrs[] = {
 	NULL,
 };

+static umode_t
+td_is_visible(struct kobject *kobj, struct attribute *attr, int i)
+{
+	/*
+	 * Hide the perf metrics topdown events
+	 * if the slots is not in CPUID.
+	 */
+	if (x86_pmu.num_topdown_events)
+		return (x86_pmu.intel_ctrl & INTEL_PMC_MSK_FIXED_SLOTS) ? attr->mode : 0;
+
+	return attr->mode;
+}
+
 static umode_t
 tsx_is_visible(struct kobject *kobj, struct attribute *attr, int i)
 {
@@ -5600,6 +5613,7 @@ default_is_visible(struct kobject *kobj, struct
attribute *attr, int i)

 static struct attribute_group group_events_td  = {
 	.name = "events",
+	.is_visible = td_is_visible,
 };

 static struct attribute_group group_events_mem = {
@@ -5758,6 +5772,23 @@ static inline int
hybrid_find_supported_cpu(struct x86_hybrid_pmu *pmu)
 	return (cpu >= nr_cpu_ids) ? -1 : cpu;
 }

+static umode_t hybrid_td_is_visible(struct kobject *kobj,
+					struct attribute *attr, int i)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct x86_hybrid_pmu *pmu =
+		 container_of(dev_get_drvdata(dev), struct x86_hybrid_pmu, pmu);
+
+	if (!is_attr_for_this_pmu(kobj, attr))
+		return 0;
+
+	/* Only check the big core which supports perf metrics */
+	if (pmu->cpu_type == hybrid_big)
+		return (pmu->intel_ctrl & INTEL_PMC_MSK_FIXED_SLOTS) ? attr->mode : 0;
+
+	return attr->mode;
+}
+
 static umode_t hybrid_tsx_is_visible(struct kobject *kobj,
 				     struct attribute *attr, int i)
 {
@@ -5784,7 +5815,7 @@ static umode_t hybrid_format_is_visible(struct
kobject *kobj,

 static struct attribute_group hybrid_group_events_td  = {
 	.name		= "events",
-	.is_visible	= hybrid_events_is_visible,
+	.is_visible	= hybrid_td_is_visible,
 };

 static struct attribute_group hybrid_group_events_mem = {


Thanks,
Kan