Messages in this thread | | | Date | Fri, 17 Jul 2015 16:47:26 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 3/9] perf/x86: Add is_hardware_event |
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On Fri, Jul 17, 2015 at 04:03:36PM +0100, Liang, Kan wrote: > > > > On Thu, Jul 16, 2015 at 09:33:45PM +0100, kan.liang@intel.com wrote: > > > From: Kan Liang <kan.liang@intel.com> > > > > > > Using is_hardware_event to replace !is_software_event to indicate a > > > hardware event. > > > > Why...? > > First, the comments of is_software_event is not correct. > 0 or !is_software_event is not for a hardware event. > is_hardware_event is for a hardware event.
Circular logic is fantastic.
> Also, the following patch make mix core_misc event be part of hw/sw > event, !is_software_event could be either hw event or core_misc event.
!is_software_event is also true for an uncore event currently, and the code relies on this fact. Blindly replacing !is_software_event with is_hardware_event changes the behaviour of the code for uncore events.
> > For an uncore event e, is_hardware_event(e) != !is_software_event(e), > > so this will be a change of behaviour... > > Uncore event cannot be part of hw/sw event group. So it doesn't change the behavior.
My complaint had _nothing_ to do with groups. It had to do with the accounting for throttling, where it _does_ change the behaviour.
However, now that you mention the group logic...
> > > /* > > > - * Return 1 for a software event, 0 for a hardware event > > > + * Return 1 for a software event, 0 for other event > > > */ > > > static inline int is_software_event(struct perf_event *event) { > > > return event->pmu->task_ctx_nr == perf_sw_context; } > > > > > > +static inline int is_hardware_event(struct perf_event *event) { > > > + return event->pmu->task_ctx_nr == perf_hw_context; } > > > + > > > extern struct static_key > > perf_swevent_enabled[PERF_COUNT_SW_MAX]; > > > > > > extern void ___perf_sw_event(u32, u64, struct pt_regs *, u64); diff > > > --git a/kernel/events/core.c b/kernel/events/core.c index > > > d3dae34..9077867 100644 > > > --- a/kernel/events/core.c > > > +++ b/kernel/events/core.c > > > @@ -1347,7 +1347,7 @@ static void perf_group_attach(struct > > perf_event *event) > > > WARN_ON_ONCE(group_leader->ctx != event->ctx); > > > > > > if (group_leader->group_flags & PERF_GROUP_SOFTWARE && > > > - !is_software_event(event)) > > > + is_hardware_event(event)) > > > group_leader->group_flags &= ~PERF_GROUP_SOFTWARE; > > >
...this changes the behaviour of attaching an uncore event to a software group.
Before, we'd correctly clear the PERF_GROUP_SOFTWARE flag on the leader. After this patch, we don't. That is a bug.
My original complaint was with the changes below.
> > > list_add_tail(&event->group_entry, &group_leader->sibling_list); > > @@ > > > -1553,7 +1553,7 @@ event_sched_out(struct perf_event *event, > > > event->pmu->del(event, 0); > > > event->oncpu = -1; > > > > > > - if (!is_software_event(event)) > > > + if (is_hardware_event(event)) > > > cpuctx->active_oncpu--; > > > if (!--ctx->nr_active) > > > perf_event_ctx_deactivate(ctx);
Previously we'd call perf_event_ctx_deactivate() for an uncore PMU's contexts, but now we never will.
> > > @@ -1881,7 +1881,7 @@ event_sched_in(struct perf_event *event, > > > goto out; > > > } > > > > > > - if (!is_software_event(event)) > > > + if (is_hardware_event(event)) > > > cpuctx->active_oncpu++; > > > if (!ctx->nr_active++) > > > perf_event_ctx_activate(ctx);
Similarly for perf_event_ctx_deactivate().
As I mention below, That means we will no longer perform throttling for an uncore PMU's cpu context (see perf_event_task_tick()).
> > ... whereby we won't accuont uncore events as active, and thereforef will > > never perform throttling. > > > > That doesn't sound right. > > I think active_oncpu should only impact if the group is exclusive. > The changes will make pure perf_invalid_context event group never exclusive. > If that's a problem, I will change this part back.
I'm not sure what you mean here -- I can't see what a group being exclusive has to do with any of the points above.
What am I missing?
Thanks, Mark.
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