Re: [kvm-unit-tests PATCH 0/6] arm: pmu: Fix random failures of pmu-chain-promotion

[Mark Rutland <mark.rutland@arm.com>]

On Tue, Apr 04, 2023 at 02:47:47PM +0200, Andrew Jones wrote:
> On Tue, Apr 04, 2023 at 08:23:15AM +0200, Eric Auger wrote:
> > Hi,
> > 
> > On 3/15/23 12:07, Eric Auger wrote:
> > > On some HW (ThunderXv2), some random failures of
> > > pmu-chain-promotion test can be observed.
> > >
> > > pmu-chain-promotion is composed of several subtests
> > > which run 2 mem_access loops. The initial value of
> > > the counter is set so that no overflow is expected on
> > > the first loop run and overflow is expected on the second.
> > > However it is observed that sometimes we get an overflow
> > > on the first run. It looks related to some variability of
> > > the mem_acess count. This variability is observed on all
> > > HW I have access to, with different span though. On
> > > ThunderX2 HW it looks the margin that is currently taken
> > > is too small and we regularly hit failure.
> > >
> > > although the first goal of this series is to increase
> > > the count/margin used in those tests, it also attempts
> > > to improve the pmu-chain-promotion logs, add some barriers
> > > in the mem-access loop, clarify the chain counter
> > > enable/disable sequence.
> > >
> > > A new 'pmu-memaccess-reliability' is also introduced to
> > > detect issues with MEM_ACCESS event variability and make
> > > the debug easier.

As a minor nit, 'pmu-mem-access-reliability' would be more consistent with
'pmu-mem-access'. The lack of a dash in 'memaccess' tripped me up while I was
trying to run those two tests.

> > > Obviously one can wonder if this variability is something normal
> > > and does not hide any other bug. I hope this series will raise
> > > additional discussions about this.
> > >
> > > https://github.com/eauger/kut/tree/pmu-chain-promotion-fixes-v1
> > 
> > Gentle ping.
> 
> I'd be happy to take this, but I was hoping to see some r-b's and/or t-b's
> from some of the others.

I gave this a spin on my ThunderX2, and it seems to fix the intermittent
failures I was seeing.

FWIW:

Tested-by: Mark Rutland <mark.rutland@arm.com>

Before (on commit 4ba7058c61e8922f9c8397cfa1095fac325f809b):

Test results below.

| [mark@gravadlaks:~/src/kvm-unit-tests]% TESTNAME=pmu-chain-promotion TIMEOUT=90s ACCEL= useapp qemu ./arm/run arm/pmu.flat -smp 1 -append 'pmu-chain-promotion'
| timeout -k 1s --foreground 90s /home/mark/.opt/apps/qemu/bin/qemu-system-aarch64 -nodefaults -machine virt,gic-version=host -accel kvm -cpu host -device virtio-serial-device -device virtconsole,chardev=ctd -chardev testdev,id=ctd -device pci-testdev -display none -serial stdio -kernel arm/pmu.flat -smp 1 -append pmu-chain-promotion # -initrd /tmp/tmp.nl1i6S0EIY
| INFO: PMU version: 0x4
| INFO: PMU implementer/ID code: 0(" ")/0
| INFO: Implements 6 event counters
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: chain counter not counting if even counter is disabled
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: odd counter did not increment on overflow if disabled
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: MEM_ACCESS counter #0 has value 0x7
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: CHAIN counter #1 has value 0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: overflow counter 0x1
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: MEM_ACCESS counter #0 has value 0x4
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: MEM_ACCESS counter #0 has value 0x1b
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: should have triggered an overflow on #0
| FAIL: pmu: pmu-chain-promotion: 32-bit overflows: CHAIN counter #1 shouldn't have incremented
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: counter #0 = 0xffffffdc, counter #1 = 0x0 overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: MEM_ACCESS counter #0 has value 0x4
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: MEM_ACCESS counter #0 has value 0x1b
| FAIL: pmu: pmu-chain-promotion: 32-bit overflows: CHAIN counter enabled: CHAIN counter was incremented and overflow
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: CHAIN counter #1 = 0x0, overflow=0x1
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: MEM_ACCESS counter #0 has value 0x4
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: MEM_ACCESS counter #0 has value 0x1b
| FAIL: pmu: pmu-chain-promotion: 32-bit overflows: 32b->64b: CHAIN counter incremented and overflow
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: CHAIN counter #1 = 0x0, overflow=0x1
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: counter #0=0xfffffff3, counter #1=0x0
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: overflow is expected on counter 0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: counter #0=0xa, counter #1=0xf9 overflow=0x1
| SUMMARY: 7 tests, 3 unexpected failures

After:

| [mark@gravadlaks:~/src/kvm-unit-tests]% TESTNAME=pmu-chain-promotion TIMEOUT=90s ACCEL=kvm useapp qemu ./arm/run arm/pmu.flat -smp 1 -append 'pmu-chain-promotion'
| timeout -k 1s --foreground 90s /home/mark/.opt/apps/qemu/bin/qemu-system-aarch64 -nodefaults -machine virt,gic-version=host -accel kvm -cpu host -device virtio-serial-device -device virtconsole,chardev=ctd -chardev testdev,id=ctd -device pci-testdev -display none -serial stdio -kernel arm/pmu.flat -smp 1 -append pmu-chain-promotion # -initrd /tmp/tmp.pahLyg1F3s
| INFO: PMU version: 0x4
| INFO: PMU implementer/ID code: 0(" ")/0
| INFO: Implements 6 event counters
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest1: post #1=0x0 #0=0x0 overflow=0x0
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: subtest1: chain counter not counting if even counter is disabled
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest2: post #1=0x0 #0=0xf3 overflow=0x1
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: subtest2: odd counter did not increment on overflow if disabled
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest3: init #1=0x0 #0=0xfffffea1 overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest3: After 1st loop #1=0x0 #0=0xffffffa0 overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest3: After 2d loop #1=0x0 #0=0xc0 overflow=0x1
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: subtest3: should have triggered an overflow on #0
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: subtest3: CHAIN counter #1 shouldn't have incremented
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest4: init #1=0x0 #0=0xfffffea1 overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest4: After 1st loop #1=0x0 #0=0xffffffb7 overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest4: After 2d loop #1=0x1 #0=0xbc overflow=0x1
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: subtest4: CHAIN counter enabled: CHAIN counter was incremented and overflow
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest5: init #1=0x0 #0=0xfffffea1 overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest5: After 1st loop #1=0x22c #0=0xffffff9f overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest5: After 2d loop #1=0x1 #0=0x9d overflow=0x1
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: subtest5: 32b->64b: CHAIN counter incremented and overflow
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest6: init #1=0x0 #0=0xfffffea1 overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest6: After 1st loop #1=0x0 #0=0xffffff9f overflow=0x0
| INFO: pmu: pmu-chain-promotion: 32-bit overflows: subtest6: After 2d loop #1=0x1f9 #0=0x9c overflow=0x1
| PASS: pmu: pmu-chain-promotion: 32-bit overflows: subtest6: overflow is expected on counter 0
| SUMMARY: 7 tests

As a bonus, the mem-access and memaccess-reliability results:

| [mark@gravadlaks:~/src/kvm-unit-tests]% TESTNAME=pmu-chain-promotion TIMEOUT=90s ACCEL=kvm useapp qemu ./arm/run arm/pmu.flat -smp 1 -append 'pmu-mem-access'     
| timeout -k 1s --foreground 90s /home/mark/.opt/apps/qemu/bin/qemu-system-aarch64 -nodefaults -machine virt,gic-version=host -accel kvm -cpu host -device virtio-serial-device -device virtconsole,chardev=ctd -chardev testdev,id=ctd -device pci-testdev -display none -serial stdio -kernel arm/pmu.flat -smp 1 -append pmu-mem-access # -initrd /tmp/tmp.84AeEp8Tiw
| INFO: PMU version: 0x4
| INFO: PMU implementer/ID code: 0(" ")/0
| INFO: Implements 6 event counters
| INFO: pmu: pmu-mem-access: 32-bit overflows: counter #0 is 0x15 (MEM_ACCESS)
| INFO: pmu: pmu-mem-access: 32-bit overflows: counter #1 is 0x15 (MEM_ACCESS)
| PASS: pmu: pmu-mem-access: 32-bit overflows: Ran 20 mem accesses
| PASS: pmu: pmu-mem-access: 32-bit overflows: Ran 20 mem accesses with expected overflows on both counters
| INFO: pmu: pmu-mem-access: 32-bit overflows: cnt#0=0x8 cnt#1=0x8 overflow=0x3
| SKIP: pmu: pmu-mem-access: 64-bit overflows: Skip test as 64 overflows need FEAT_PMUv3p5
| SUMMARY: 3 tests, 1 skipped
| [mark@gravadlaks:~/src/kvm-unit-tests]% TESTNAME=pmu-chain-promotion TIMEOUT=90s ACCEL=kvm useapp qemu ./arm/run arm/pmu.flat -smp 1 -append 'pmu-memaccess-reliability'
| timeout -k 1s --foreground 90s /home/mark/.opt/apps/qemu/bin/qemu-system-aarch64 -nodefaults -machine virt,gic-version=host -accel kvm -cpu host -device virtio-serial-device -device virtconsole,chardev=ctd -chardev testdev,id=ctd -device pci-testdev -display none -serial stdio -kernel arm/pmu.flat -smp 1 -append pmu-memaccess-reliability # -initrd /tmp/tmp.ZToqwencZR
| INFO: PMU version: 0x4
| INFO: PMU implementer/ID code: 0(" ")/0
| INFO: Implements 6 event counters
| INFO: pmu: pmu-memaccess-reliability: 32-bit overflows: overflow=0 min=251 max=283 COUNT=250 MARGIN=100
| PASS: pmu: pmu-memaccess-reliability: 32-bit overflows: memaccess is reliable
| SKIP: pmu: pmu-memaccess-reliability: 64-bit overflows: Skip test as 64 overflows need FEAT_PMUv3p5
| SUMMARY: 2 tests, 1 skipped

Thanks,
Mark.