Re: [PATCH] perf tests record: allow for some difference in cycle count in leader sampling test on aarch64

[Thomas Richter <tmricht@linux.ibm.com>]

On 10/2/25 15:39, Anubhav Shelat wrote:
> On Oct 1, 2025 at 9:44 PM, Ian Rogers wrote:
>> If cycles is 0 then this will always pass, should this be checking a
> range?
> 
> Yes you're right this will be better.
> 
> On Oct 2, 2025 at 7:56 AM, Thomas Richter wrote:
>> Can we use a larger range to allow the test to pass?
> 
> What range do you get on s390? When I do group measurements using "perf
> record -e "{cycles,cycles}:Su" perf test -w brstack" like in the test I
> always get somewhere between 20 and 50 cycles difference. I haven't tested
> on s390x, but I see no cycle count difference when testing the same command
> on x86. I have observed much larger, more varied differences when using
> software events.
> 
> Anubhav
> 

Here is the output of the 

 # perf record  -e "{cycles,cycles}:Su" -- ./perf test -w brstack 
 # perf script | grep brstack

commands:

perf 1110782 426394.696874:    6885000 cycles:           116fc9e brstack_bench+0xae (/r>
perf 1110782 426394.696875:    1377000 cycles:           116fb98 brstack_foo+0x0 (/root>
perf 1110782 426394.696877:    1377000 cycles:           116fb48 brstack_bar+0x0 (/root>
perf 1110782 426394.696878:    1377000 cycles:           116fc94 brstack_bench+0xa4 (/r>
perf 1110782 426394.696880:    1377000 cycles:           116fc84 brstack_bench+0x94 (/r>
perf 1110782 426394.696881:    1377000 cycles:           116fb7c brstack_bar+0x34 (/roo>
perf 1110782 426394.696883:    1377000 cycles:           116fb7c brstack_bar+0x34 (/roo>
perf 1110782 426394.696884:    1377000 cycles:           116fb7c brstack_bar+0x34 (/roo>
perf 1110782 426394.696885:    1377000 cycles:           116fb7c brstack_bar+0x34 (/roo>
perf 1110782 426394.696887:    1377000 cycles:           116fb7c brstack_bar+0x34 (/roo>
perf 1110782 426394.696888:    1377000 cycles:           116fc98 brstack_bench+0xa8 (/r>
perf 1110782 426394.696890:    1377000 cycles:           116fb7c brstack_bar+0x34 (/roo>
perf 1110782 426394.696891:    1377000 cycles:           116fc9e brstack_bench+0xae (/r>
perf 1110782 426394.703542:    1377000 cycles:           116fb7c brstack_bar+0x34 (/roo>
perf 1110782 426394.703542:   30971975 cycles:           116fb7c brstack_bar+0x34 (/roo>
perf 1110782 426394.703543:    1377000 cycles:           116fc76 brstack_bench+0x86 (/r>
perf 1110782 426394.703545:    1377000 cycles:           116fc06 brstack_bench+0x16 (/r>
perf 1110782 426394.703546:    1377000 cycles:           116fc9e brstack_bench+0xae (/r>
perf 1110782 426394.703547:    1377000 cycles:           116fc20 brstack_bench+0x30 (/r>
perf 1110782 426394.703549:    1377000 cycles:           116fc9e brstack_bench+0xae (/r>
perf 1110782 426394.703550:    1377000 cycles:           116fcbc brstack_bench+0xcc

They are usual identical values beside one or two which are way off. Ignoring those would
be good.

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

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