Re: [PATCH 05/11] perf: New PERF_EVENT_IOC_INJECT ioctl

[Frederic Weisbecker <fweisbec@gmail.com>]

On Wed, Feb 03, 2010 at 10:14:29AM +0100, Frederic Weisbecker wrote:
> The PERF_EVENT_IOC_INJECT perf event ioctl can be used to inject
> events, if the corresponding pmu and event supports it.
> 
> On trace events, it will call the inject callback, usually reserved
> for events that need to catch up with the user.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
> Cc: Li Zefan <lizf@cn.fujitsu.com>
> Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
> Cc: Masami Hiramatsu <mhiramat@redhat.com>
> Cc: Jens Axboe <jens.axboe@oracle.com>
> ---
>  include/linux/perf_event.h |    2 ++
>  kernel/perf_event.c        |   23 +++++++++++++++++++++++
>  2 files changed, 25 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 556b0f4..d2e83f0 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -228,6 +228,7 @@ struct perf_event_attr {
>  #define PERF_EVENT_IOC_PERIOD		_IOW('$', 4, __u64)
>  #define PERF_EVENT_IOC_SET_OUTPUT	_IO ('$', 5)
>  #define PERF_EVENT_IOC_SET_FILTER	_IOW('$', 6, char *)
> +#define PERF_EVENT_IOC_INJECT		_IO ('$', 7)
>  
>  enum perf_event_ioc_flags {
>  	PERF_IOC_FLAG_GROUP		= 1U << 0,
> @@ -513,6 +514,7 @@ struct pmu {
>  	void (*disable)			(struct perf_event *event);
>  	void (*read)			(struct perf_event *event);
>  	void (*unthrottle)		(struct perf_event *event);
> +	void (*inject)			(struct perf_event *event);
>  };
>  
>  /**
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index 40f8b07..e4dfd12 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -2151,6 +2151,26 @@ unlock:
>  	return ret;
>  }
>  
> +static void __perf_event_inject(void *info)
> +{
> +	struct perf_event *event = info;
> +
> +	event->pmu->inject(event);
> +}
> +
> +static int perf_event_inject(struct perf_event *event)
> +{
> +	struct perf_event_context *ctx = event->ctx;
> +	struct task_struct *task = ctx->task;
> +
> +	if (!event->pmu->inject || task)
> +		return -EINVAL;
> +
> +	smp_call_function_single(event->cpu, __perf_event_inject, event, 1);
> +



Ah, I forgot to say. Injection is only supported on cpu
bound events (non-task bound). Because if it is task-bound,
we can't ensure we can inject while the event is scheduled,
not sure how to fix this.