[Skiboot] [RFC PATCH] core/opal: Add OPAL call statistics

[Naveen N. Rao]

Cédric Le Goater wrote:
> On 2/29/20 10:27 AM, Nicholas Piggin wrote:
>> Cédric Le Goater's on February 29, 2020 4:34 am:
>>> Here is a proposal to collect OPAL call statistics, counts and duration,
>>> and track areas we could possibly improve.
>>>
>>> With a small Linux driver to dump the stats in debugfs, here is what
>>> we get on a P9 after boot:
>> 
>> Seems interesting... you could just do it all on the Linux side though.
> 
> I thought we might collect more data from OPAL in opal_exit. 

As Nick points out, this can be done from Linux through the use of 
tracepoints. We already have similar statistics for hcalls through a 
perf script. A similar script should be able to support OPAL calls.

See:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/scripts/python/powerpc-hcalls.py

> 
>> Any reason you want these stats? 
> 
> HW configuration (XIVE) is in mind but it could be applied to other 
> areas.
> 
> 1. To see which calls are being used and how frequently 
> 2. to track average and max values which would reflect issues in 
>    OPAL, locking or polling.
> 3. to see impact of some changes
> 
>> I'd like to try get basic perf and possibly even ftrace support for 
>> OPAL (driven from Linux). It's still a way off but coming along slowly.

By 'perf', do you mean PMU support?
I guess we already have basic _mcount() support in skiboot. Do you plan 
to have this data be fed to Linux ftrace in some manner? Would be good 
to hear your plans.


Thanks,
Naveen