On 7/21/2020 9:10 AM, Peter Zijlstra wrote:
On Fri, Jul 17, 2020 at 07:05:51AM -0700, [email protected] wrote:
From: Kan Liang <[email protected]>
Users fail to sample-read the slots and metrics events, e.g.,
perf record -e '{slots, topdown-retiring}:S'.
When reading the metrics event, the fixed counter 3 (slots) has to be
reset, which impacts the sampling of the slots event.
Add a specific validate_group() support to reject the case and error out
for Ice Lake.
An alternative fix may unconditionally disable slots sampling, but it's
not a decent fix. Users may want to only sample the slot events
without the topdown metrics events.
Signed-off-by: Kan Liang <[email protected]>
I'm confused by this; it doesn't make sense.
Should not patch 7 have something like the below instead?
> Also, I think there is a bug when we create a group like this and then
kill the leader, in that case the core code will 'promote' the sibling
metric events to their own individual events, see perf_group_detach().
I'm trying to produce the bug mentioned above, but I'm not sure under
what situation, the core code will 'promote' the sibling metric events?
I tried the suggested code below. It works well for the sample-read
case. Perf tool errors out as expected.
perf record -e '{slots,topdown-fe-bound}:S' sleep 1
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument)
for event (topdown-fe-bound).
/bin/dmesg | grep -i perf may provide additional information.
Thanks,
Kan
We need additional code to move those events into unrecoverable ERROR
state. A new group_caps flag could indicate this promotion isn't
allowed.
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3441,8 +3441,22 @@ static int intel_pmu_hw_config(struct pe
* A flag PERF_X86_EVENT_TOPDOWN is applied for the case.
*/
if (x86_pmu.intel_cap.perf_metrics && is_topdown_event(event)) {
- if (is_metric_event(event) && is_sampling_event(event))
- return -EINVAL;
+
+ if (is_metric_event(event)) {
+ struct perf_event *leader = event->group_leader;
+
+ if (is_sampling_event(event))
+ return -EINVAL;
+
+ if (leader == event)
+ return -EINVAL;
+
+ if (!is_slots_event(leader))
+ return -EINVAL;
+
+ if (is_sampling_event(leader))
+ return -EINVAL;
+ }
if (!is_sampling_event(event)) {
if (event->attr.config1 != 0)
