Re: [PATCH] perf stat: Support per-cluster aggregation

[Yicong Yang]

Hi Tim,

On 2023/3/25 2:05, Chen, Tim C wrote:
>>
>> From: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
>>
>> Some platforms have 'cluster' topology and CPUs in the cluster will share
>> resources like L3 Cache Tag (for HiSilicon Kunpeng SoC) or L2 cache (for Intel
>> Jacobsville). Currently parsing and building cluster topology have been
>> supported since [1].
>>
>> perf stat has already supported aggregation for other topologies like die or
>> socket, etc. It'll be useful to aggregate per-cluster to find problems like L3T
>> bandwidth contention or imbalance.
>>
>> This patch adds support for "--per-cluster" option for per-cluster aggregation.
>> Also update the docs and related test. The output will be like:
>>
>> [root@localhost tmp]# perf stat -a -e LLC-load --per-cluster -- sleep 5
>>
>> Performance counter stats for 'system wide':
>>
>> S56-D0-CLS158    4      1,321,521,570      LLC-load
>> S56-D0-CLS594    4        794,211,453      LLC-load
>> S56-D0-CLS1030    4             41,623      LLC-load
>> S56-D0-CLS1466    4             41,646      LLC-load
>> S56-D0-CLS1902    4             16,863      LLC-load
>> S56-D0-CLS2338    4             15,721      LLC-load
>> S56-D0-CLS2774    4             22,671      LLC-load
>> [...]
> 
> Overall it looks good.  You can add my reviewed-by.
> 

thanks.

> I wonder if we could enhance the help message 
> in perf stat to tell user to refer to 
> /sys/devices/system/cpu/cpuX/topology/*_id
> to map relevant ids back to overall cpu topology.
> 
> For example the above example, cluster S56-D0-CLS158  has
> really heavy load. It took me  a while
> going through the code to figure out how to find
> the info that maps cluster id to cpu.
> 

yes, indeed. Actually this is because my bios doesn't report a valid
ID for these topologies so the ACPI use the offset of the topology
node in the PPTT as a fallback. Other topologies also suffers the same:

On my machine:
[root@localhost debug]# perf stat --per-socket -e cycles -a -- sleep 1

 Performance counter stats for 'system wide':

S56      64         21,563,375      cycles
S7182    64         32,140,641      cycles

       1.008520310 seconds time elapsed

On x86:
root@ubuntu204:/home/yang/linux/tools/perf# ./perf stat -a --per-socket -e cycles -- sleep 1

 Performance counter stats for 'system wide':

S0       40        137,205,897      cycles
S1       40         67,720,731      cycles

       1.003546720 seconds time elapsed

Maybe I can try to add a separate patch for describing the source of the
topology ids in the perf manual.

Thanks,
Yicong