linux-kernel - Re: [PATCH 3/9] perf/x86: Add is_hardware

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Date:	Fri, 17 Jul 2015 11:48:14 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	"kan.liang@...el.com" <kan.liang@...el.com>
Cc:	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"eranian@...gle.com" <eranian@...gle.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"adrian.hunter@...el.com" <adrian.hunter@...el.com>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/9] perf/x86: Add is_hardware_event

On Thu, Jul 16, 2015 at 09:33:45PM +0100, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> Using is_hardware_event to replace !is_software_event to indicate a
> hardware event.

Why...?

For an uncore event e, is_hardware_event(e) != !is_software_event(e), so
this will be a change of behaviour...

> 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  include/linux/perf_event.h | 7 ++++++-
>  kernel/events/core.c       | 6 +++---
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 2027809..fea0ddf 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -761,13 +761,18 @@ static inline bool is_sampling_event(struct perf_event *event)
>  }
>  
>  /*
> - * 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;
>  
>  	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);
> @@ -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);

... whereby we won't accuont uncore events as active, and thereforef
will never perform throttling.

That doesn't sound right.

Mark.
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