perf/x86/intel: make error messages less confusing

PATCH In review Eduardo Valentin 3 participants 8 messages Aug 23, 2018 – Sep 14, 2018

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x86 perf events

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Eduardo Valentin

author

2018-08-23 15:07 UTC #0 lore raw

PATCH v2 1/1 perf/x86/intel: make error messages less confusing

On a system with X86_FEATURE_ARCH_PERFMON disabled and with a model not known by family PMU drivers, user gets a kernel message log like the following:

[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.

The "unsupported .. CPU" part may be confusing for some users leading to wrong understanding that the kernel does not support the CPU model.

This patch rewords the messages on the failure path to:

[ 0.667154] Performance Events: CPU does not support PMU: no PMU driver, software events only.

Cc Thomas Gleixner <[email protected]>

Cc Ingo Molnar <[email protected]>

Cc "H. Peter Anvin" <[email protected]>

Cc [email protected]

Cc Peter Zijlstra <[email protected]>

Cc Andi Kleen <[email protected]>

Cc Kan Liang <[email protected]>

Cc Dan Carpenter <[email protected]>

Cc Eduardo Valentin <[email protected]>

Cc Jia Zhang <[email protected]>

Cc Greg Kroah-Hartman <[email protected]>

Cc [email protected]

Signed-off-by Eduardo Valentin <[email protected]>

---

Changes from V1->V2:
- As per initial review, the propose messaging was even more confusing. Simplified it by only saying that the CPU does not support PMU.

 arch/x86/events/intel/core.c | 15 +++++++++++----
 arch/x86/events/intel/p4.c   |  5 +----
 arch/x86/events/intel/p6.c   |  1 -
 3 files changed, 12 insertions(+), 9 deletions(-)

arch/x86/events/intel/core.c +11 -4

index 035c37481f57..2ddb97f03f4a 100644
@@ -3889,15 +3889,22 @@ __init int intel_pmu_init(void)
 	char *name;
 
 	if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
+		int ret = -ENODEV;
+
 		switch (boot_cpu_data.x86) {
 		case 0x6:
-			return p6_pmu_init();
+			ret = p6_pmu_init();
+			break;
 		case 0xb:
-			return knc_pmu_init();
+			ret = knc_pmu_init();
+			break;
 		case 0xf:
-			return p4_pmu_init();
+			ret = p4_pmu_init();
+			break;
 		}
-		return -ENODEV;
+		if (ret)
+			pr_cont("CPU does not support PMU: ");
+		return ret;
 	}
 
 	/*

arch/x86/events/intel/p4.c +1 -4

index d32c0eed38ca..fb5e8576d9ac 100644
@@ -1345,11 +1345,8 @@ __init int p4_pmu_init(void)
 	BUILD_BUG_ON(ARCH_P4_MAX_CCCR > INTEL_PMC_MAX_GENERIC);
 
 	rdmsr(MSR_IA32_MISC_ENABLE, low, high);
-	if (!(low & (1 << 7))) {
-		pr_cont("unsupported Netburst CPU model %d ",
-			boot_cpu_data.x86_model);
+	if (!(low & (1 << 7)))
 		return -ENODEV;
-	}
 
 	memcpy(hw_cache_event_ids, p4_hw_cache_event_ids,
 		sizeof(hw_cache_event_ids));

arch/x86/events/intel/p6.c +0 -1

index 408879b0c0d4..e8e03e68b22f 100644
@@ -269,7 +269,6 @@ __init int p6_pmu_init(void)
 		break;
 
 	default:
-		pr_cont("unsupported p6 CPU model %d ", boot_cpu_data.x86_model);
 		return -ENODEV;
 	}

Signature · 1 line

2.18.0

Eduardo Valentin

author

2018-09-04 18:33 UTC #1 lore raw

Hello,

Quoted 12 lines · Eduardo Valentin

On a system with X86_FEATURE_ARCH_PERFMON disabled and with a model not known by family PMU drivers, user gets a kernel message log like the following:
[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.
The "unsupported .. CPU" part may be confusing for some users leading to wrong understanding that the kernel does not support the CPU model.
This patch rewords the messages on the failure path to:
[ 0.667154] Performance Events: CPU does not support PMU: no PMU driver, software events only.

Gentle ping on this patch, any further comments?

Quoted 89 lines

Cc Thomas Gleixner <[email protected]>

Cc Ingo Molnar <[email protected]>

Cc "H. Peter Anvin" <[email protected]>

Cc [email protected]

Cc Peter Zijlstra <[email protected]>

Cc Andi Kleen <[email protected]>

Cc Kan Liang <[email protected]>

Cc Dan Carpenter <[email protected]>

Cc Eduardo Valentin <[email protected]>

Cc Jia Zhang <[email protected]>

Cc Greg Kroah-Hartman <[email protected]>

Cc [email protected]

Signed-off-by Eduardo Valentin <[email protected]>

---

Changes from V1->V2:
- As per initial review, the propose messaging was even more confusing. Simplified it by only saying that the CPU does not support PMU.

 arch/x86/events/intel/core.c | 15 +++++++++++----
 arch/x86/events/intel/p4.c   |  5 +----
 arch/x86/events/intel/p6.c   |  1 -
 3 files changed, 12 insertions(+), 9 deletions(-)

arch/x86/events/intel/core.c +11 -4

index 035c37481f57..2ddb97f03f4a 100644
@@ -3889,15 +3889,22 @@ __init int intel_pmu_init(void)
 	char *name;
 
 	if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
+		int ret = -ENODEV;
+
 		switch (boot_cpu_data.x86) {
 		case 0x6:
-			return p6_pmu_init();
+			ret = p6_pmu_init();
+			break;
 		case 0xb:
-			return knc_pmu_init();
+			ret = knc_pmu_init();
+			break;
 		case 0xf:
-			return p4_pmu_init();
+			ret = p4_pmu_init();
+			break;
 		}
-		return -ENODEV;
+		if (ret)
+			pr_cont("CPU does not support PMU: ");
+		return ret;
 	}
 
 	/*

arch/x86/events/intel/p4.c +1 -4

index d32c0eed38ca..fb5e8576d9ac 100644
@@ -1345,11 +1345,8 @@ __init int p4_pmu_init(void)
 	BUILD_BUG_ON(ARCH_P4_MAX_CCCR > INTEL_PMC_MAX_GENERIC);
 
 	rdmsr(MSR_IA32_MISC_ENABLE, low, high);
-	if (!(low & (1 << 7))) {
-		pr_cont("unsupported Netburst CPU model %d ",
-			boot_cpu_data.x86_model);
+	if (!(low & (1 << 7)))
 		return -ENODEV;
-	}
 
 	memcpy(hw_cache_event_ids, p4_hw_cache_event_ids,
 		sizeof(hw_cache_event_ids));

arch/x86/events/intel/p6.c +0 -1

index 408879b0c0d4..e8e03e68b22f 100644
@@ -269,7 +269,6 @@ __init int p6_pmu_init(void)
 		break;
 
 	default:
-		pr_cont("unsupported p6 CPU model %d ", boot_cpu_data.x86_model);
 		return -ENODEV;
 	}

Signature · 1 line

2.18.0

Signature · 2 lines

All the best,
Eduardo Valentin

Andi Kleen

Reviewed-by

2018-09-04 23:04 UTC #2 lore raw

Quoted 12 lines · Eduardo Valentin

Hello,
Quoted 9 lines · Eduardo Valentin
On a system with X86_FEATURE_ARCH_PERFMON disabled and with a model not known by family PMU drivers, user gets a kernel message log like the following:
[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.
The "unsupported .. CPU" part may be confusing for some users leading to wrong understanding that the kernel does not support the CPU model.

Quoted 6 lines

Quoted 3 lines
This patch rewords the messages on the failure path to:
[ 0.667154] Performance Events: CPU does not support PMU: no PMU driver, software events only.
Gentle ping on this patch, any further comments?

Reviewed-by Andi Kleen <[email protected]>

-Andi

Peter Zijlstra

maintainer

2018-09-05 08:52 UTC #3 lore raw

In reply to Eduardo Valentin

Quoted 8 lines · Eduardo Valentin

On a system with X86_FEATURE_ARCH_PERFMON disabled and with a model not known by family PMU drivers, user gets a kernel message log like the following:
[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.
The "unsupported .. CPU" part may be confusing for some users leading to wrong understanding that the kernel does not support the CPU model.

Send them back to first grade, such that they might learn to read?

Eduardo Valentin

author

2018-09-05 16:03 UTC #4 lore raw

Quoted 6 lines · Peter Zijlstra

Quoted 5 lines · Eduardo Valentin
On a system with X86_FEATURE_ARCH_PERFMON disabled and with a model not known by family PMU drivers, user gets a kernel message log like the following:
[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.

Quoted 6 lines

Quoted 3 lines
The "unsupported .. CPU" part may be confusing for some users leading to wrong understanding that the kernel does not support the CPU model.
Send them back to first grade, such that they might learn to read?

:-)

Signature · 2 lines

All the best,
Eduardo Valentin

Andi Kleen

2018-09-05 21:47 UTC #5 lore raw

Quoted 7 lines · Eduardo Valentin

Quoted 6 lines · Peter Zijlstra
Quoted 5 lines · Eduardo Valentin
On a system with X86_FEATURE_ARCH_PERFMON disabled and with a model not known by family PMU drivers, user gets a kernel message log like the following:
[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.

Quoted 8 lines

Quoted 6 lines
Quoted 3 lines
The "unsupported .. CPU" part may be confusing for some users leading to wrong understanding that the kernel does not support the CPU model.
Send them back to first grade, such that they might learn to read?
:-)

I think it's a valid concern, I guess Eduardo actually has real people who got confused.

-Andi

Peter Zijlstra

maintainer

2018-09-06 07:22 UTC #6 lore raw

Quoted 12 lines · Andi Kleen

Quoted 11 lines · Eduardo Valentin
Quoted 10 lines · Peter Zijlstra
Quoted 8 lines · Eduardo Valentin
On a system with X86_FEATURE_ARCH_PERFMON disabled and with a model not known by family PMU drivers, user gets a kernel message log like the following:
[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.
The "unsupported .. CPU" part may be confusing for some users leading to wrong understanding that the kernel does not support the CPU model.

Quoted 7 lines

Quoted 4 lines
Quoted 2 lines
Send them back to first grade, such that they might learn to read?
:-)
I think it's a valid concern, I guess Eduardo actually has real people who got confused.

But it is really easy to confuse real people; as real people are mostly clueless. There is only so much you can do for the semi illiterate masses. Should we dumb down everything to baby talk just to cater to them?

The string is clearly prefixed by the subsystem, if you get confused by that your reading comprehension really is rock bottom.

  [ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.

Heck, it even mentions "no PMU driver", how much clues do you need? Also, the proposed alternative:

  [ 0.667154] Performance Events: CPU does not support PMU: no PMU driver, software events only.

Looses out information on which CPU family we failed on. Nor does it mention the most likely reason for this error: virt crap.

I'd not mind a warning like:

[] Performance Events: Your crappy virt solution is lying about it's CPU model, it doesn't have a (matching) PMU.

Eduardo Valentin

author

2018-09-14 00:01 UTC #7 lore raw

Hey Peter,

Quoted 26 lines · Peter Zijlstra

Quoted 12 lines · Andi Kleen
Quoted 11 lines · Eduardo Valentin
Quoted 10 lines · Peter Zijlstra
Quoted 8 lines · Eduardo Valentin
On a system with X86_FEATURE_ARCH_PERFMON disabled and with a model not known by family PMU drivers, user gets a kernel message log like the following:
[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.
The "unsupported .. CPU" part may be confusing for some users leading to wrong understanding that the kernel does not support the CPU model.
Quoted 7 lines
Quoted 4 lines
Quoted 2 lines
Send them back to first grade, such that they might learn to read?
:-)
I think it's a valid concern, I guess Eduardo actually has real people who got confused.
But it is really easy to confuse real people; as real people are mostly clueless. There is only so much you can do for the semi illiterate masses. Should we dumb down everything to baby talk just to cater to them?

Quoted 5 lines

The string is clearly prefixed by the subsystem, if you get confused by that your reading comprehension really is rock bottom.
  [ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.

Once again, the confusing part is the "unsupported CPU".

Quoted 6 lines

Heck, it even mentions "no PMU driver", how much clues do you need? Also, the proposed alternative:
  [ 0.667154] Performance Events: CPU does not support PMU: no PMU driver, software events only.
Looses out information on which CPU family we failed on. Nor does it

Maybe keeping the CPU family and rephrasing the unsupported part?

Quoted 6 lines

mention the most likely reason for this error: virt crap.
I'd not mind a warning like:
[] Performance Events: Your crappy virt solution is lying about it's CPU model, it doesn't have a (matching) PMU.

Well, I would be OK if the kernel spits out a message saying that vPMU is disabled or something. That would be more accurate than unsupported CPU.

Quoted 2 lines

Signature · 2 lines

All the best,
Eduardo Valentin