[RFC, powerpc] perf/hv-24x7 set the attr group to NULL if events failed to be initialized

[Michael Ellerman]

On Wed, 2015-03-25 at 11:41 -0700, Sukadev Bhattiprolu wrote:
> Michael Ellerman [mpe at ellerman.id.au] wrote:
> | On Sun, 2015-15-02 at 09:42:57 UTC, Li Zhong wrote:
> | > This patch moves the three events groups to the end of the attr groups,
> | > and if create_events_from_catalog() fails to set their attributes, we
> | > set them to NULL in attr_groups.
> | 
> | But why are we continuing at all if create_events_from_catalog() fails?
> | 
> | Shouldn't that just be a fatal error and we bail?
> 
> Well, even if create_events_from_catalog() fails, we can continue to use
> the 24x7 events, rather clumsily, as long as the catalog is readable.  i.e.
> parse /sys/bus/event_source/devices/hv_24x7/interface/catalog to find event
> offset and run:
> 
> 	perf stat -C 0 -e hv_24x7/domain=2,offset=8,core=0/ workload


Yeah I guess, but is that really useful? And is it a case we want to support?

It seems to me if create_events_from_catalog() fails then we either have:
  - a kernel bug
  - some sort of hypervisor misconfiguration
  - ENOMEM (in which case the system's probably dead anyway)

So in all cases trying to continue on seems fairly pointless to me.

cheers