Re: [RFC PATCH 16/20] famfs: Add fault counters

[Dave Hansen]

On 2/23/24 12:39, John Groves wrote:
>> We had similar unit test regression concerns with fsdax where some
>> upstream change silently broke PMD faults. The solution there was trace
>> points in the fault handlers and a basic test that knows apriori that it
>> *should* be triggering a certain number of huge faults:
>>
>> https://github.com/pmem/ndctl/blob/main/test/dax.sh#L31
> Good approach, thanks Dan! My working assumption is that we'll be able to make
> that approach work in the famfs tests. So the fault counters should go away
> in the next version.

I do really suspect there's something more generic that should be done
here.  Maybe we need a generic 'huge_faults' perf event to pair up with
the good ol' faults that we already have:

# perf stat -e faults /bin/ls

 Performance counter stats for '/bin/ls':

               104      faults


       0.001499862 seconds time elapsed

       0.001490000 seconds user
       0.000000000 seconds sys