Re: [PATCH 2/7] perf: Introduce hw_perf_event->tp_target and ->tp_list

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Oleg Nesterov <oleg@redhat.com> [2013-02-04 20:02:46]:

> sys_perf_event_open()->perf_init_event(event) is called before
> find_get_context(event), this means that event->ctx == NULL when
> class->reg(TRACE_REG_PERF_REGISTER/OPEN) is called and thus it
> can't know if this event is per-task or system-wide.
> 
> This patch adds hw_perf_event->tp_target for PERF_TYPE_TRACEPOINT,
> this is analogous to PERF_TYPE_BREAKPOINT/bp_target we already have.
> The patch also moves ->bp_target up so that it can overlap with the
> new member, this can help the compiler to generate the better code.
> 
> trace_uprobe_register() will use it for prefiltering to avoid the
> unnecessary breakpoints in mm's we do not want to trace.
> 
> ->tp_target doesn't have its own reference, but we can rely on the
> fact that either sys_perf_event_open() holds a reference, or it is
> equal to event->ctx->task. So this pointer is always valid until
> free_event().
> 
> Also add the "struct list_head tp_list" into this union. It is not
> strictly necessary, but it can simplify the next changes and we can
> add it for free.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  include/linux/perf_event.h |    9 +++++++--
>  kernel/events/core.c       |    5 ++++-
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 6bfb2fa..c9775e9 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -135,16 +135,21 @@ struct hw_perf_event {
>  		struct { /* software */
>  			struct hrtimer	hrtimer;
>  		};
> +		struct { /* tracepoint */
> +			struct task_struct	*tp_target;
> +			/* for tp_event->class */
> +			struct list_head	tp_list;
> +		};
>  #ifdef CONFIG_HAVE_HW_BREAKPOINT
>  		struct { /* breakpoint */
> -			struct arch_hw_breakpoint	info;
> -			struct list_head		bp_list;
>  			/*
>  			 * Crufty hack to avoid the chicken and egg
>  			 * problem hw_breakpoint has with context
>  			 * creation and event initalization.
>  			 */
>  			struct task_struct		*bp_target;
> +			struct arch_hw_breakpoint	info;
> +			struct list_head		bp_list;
>  		};
>  #endif
>  	};
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 1b2e516..340fb53 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6162,11 +6162,14 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> 
>  	if (task) {
>  		event->attach_state = PERF_ATTACH_TASK;
> +
> +		if (attr->type == PERF_TYPE_TRACEPOINT)
> +			event->hw.tp_target = task;
>  #ifdef CONFIG_HAVE_HW_BREAKPOINT
>  		/*
>  		 * hw_breakpoint is a bit difficult here..
>  		 */
> -		if (attr->type == PERF_TYPE_BREAKPOINT)
> +		else if (attr->type == PERF_TYPE_BREAKPOINT)
>  			event->hw.bp_target = task;
>  #endif
>  	}
> -- 
> 1.5.5.1
> 

-- 
Thanks and Regards
Srikar Dronamraju