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

[Eric Auger <eric.auger@redhat.com>]

Hi Alexandru,
On 4/19/23 11:39, Alexandru Elisei wrote:
> Hi,
>
> On Wed, Apr 19, 2023 at 09:32:10AM +0200, Eric Auger wrote:
>> Hi,
>>
>> On 4/12/23 10:47, Mark Rutland wrote:
>>> 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.
>> I can easily respin with that renaming. thanks for the feedback. Waiting
>> a little bit more if somebody has any other comment.
> Started reviewing the series last week, something came up and I had to stop
> after the first patch (very nice improvement, by the way). I will finish
> the review by the end of this week.

OK no problem. Thanks for your time.

Eric
>
> Thanks,
> Alex
>
>> Eric
>>>>>> 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.
>>>