[PATCH 0/2] perf_events: fix the fix for transaction recovery in group_sched_in() (v2)

[Stephane Eranian <eranian@google.com>]

This is a new version of the patch to fix the way timing is handled
in group_sched_in().

Although the patch solved the issue with time_running, time_enabled
for all events in a group, it had one flaw in case the group could
never be scheduled. It would cause time_enabled to get negative.
The issue was that tstamp_stopped was never updated, even though
tstamp_enabled was.

This new version is much simpler and ensures that in case of
error in group_sched_in() during event_sched_in(), the events up
to the failed event go through regular event_sched_out(). But the
failed event and the remaining events in the group have their timings
adjusted as if they had also gone through event_sched_in() and
event_sched_out(). This ensures timing uniformity across all
events in a group. This also takes care of the tstamp_stopped problem
in case the group could never be scheduled. The tstamp_stopped is
updated as if the event had actually run.

With this patch, the following now reports correct time_enabled,
in case the NMI watchdog is active:

$ task -e unhalted_core_cycles,instructions_retired,baclears,baclears  noploop 1
noploop for 1 seconds

0 unhalted_core_cycles (100.00% scaling, ena=997,552,872, run=0)
0 instructions_retired (100.00% scaling, ena=997,552,872, run=0)
0 baclears (100.00% scaling, ena=997,552,872, run=0)
0 baclears (100.00% scaling, ena=997,552,872, run=0)

[PATCH 0/2] : introduction
[PATCH 1/2] : revert commit 8e5fc1a
[PATCH 2/2] : the actual fix

Signed-off-by: Stephane Eranian <eranian@google.com>
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