perf: Introduce hw_perf_event->tp_target and ->tp_list
Oleg Nesterov [Sat, 2 Feb 2013 15:27:52 +0000 (16:27 +0100)]
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>

include/linux/perf_event.h
kernel/events/core.c

index 42adf01..e47ee46 100644 (file)
@@ -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
        };
index 301079d..e2d4323 100644 (file)
@@ -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
        }