perf/trace: Add ability to set a target task for events

A few events are interesting not only for a current task.
For example, sched_stat_* events are interesting for a task
which wakes up. For this reason, it will be good if such
events will be delivered to a target task too.

Now a target task can be set by using __perf_task().

The original idea and a draft patch belongs to Peter Zijlstra.

I need these events for profiling sleep times. sched_switch is used for
getting callchains and sched_stat_* is used for getting time periods.
These events are combined in user space, then it can be analyzed by
perf tools.

Inspired-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arun Sharma <asharma@fb.com>
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1342016098-213063-1-git-send-email-avagin@openvz.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 38 insertions, 4 deletions

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 6581a040f39..98d4597f43d 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -153,7 +153,8 @@ put_callchain_entry(int rctx)
         put_recursion_context(__get_cpu_var(callchain_recursion), rctx);
 }
 
-struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
+struct perf_callchain_entry *
+perf_callchain(struct perf_event *event, struct pt_regs *regs)
 {
         int rctx;
         struct perf_callchain_entry *entry;
@@ -178,6 +179,12 @@ struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
         }
 
         if (regs) {
+                /*
+                 * Disallow cross-task user callchains.
+                 */
+                if (event->ctx->task && event->ctx->task != current)
+                        goto exit_put;
+
                 perf_callchain_store(entry, PERF_CONTEXT_USER);
                 perf_callchain_user(entry, regs);
         }
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f1cf0edeb39..b7935fcec7d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4039,7 +4039,7 @@ void perf_prepare_sample(struct perf_event_header *header,
         if (sample_type & PERF_SAMPLE_CALLCHAIN) {
                 int size = 1;
 
-                data->callchain = perf_callchain(regs);
+                data->callchain = perf_callchain(event, regs);
 
                 if (data->callchain)
                         size += data->callchain->nr;
@@ -5209,7 +5209,8 @@ static int perf_tp_event_match(struct perf_event *event,
 }
 
 void perf_tp_event(u64 addr, u64 count, void *record, int entry_size,
-                   struct pt_regs *regs, struct hlist_head *head, int rctx)
+                   struct pt_regs *regs, struct hlist_head *head, int rctx,
+                   struct task_struct *task)
 {
         struct perf_sample_data data;
         struct perf_event *event;
@@ -5228,6 +5229,31 @@ void perf_tp_event(u64 addr, u64 count, void *record, int entry_size,
                         perf_swevent_event(event, count, &data, regs);
         }
 
+        /*
+         * If we got specified a target task, also iterate its context and
+         * deliver this event there too.
+         */
+        if (task && task != current) {
+                struct perf_event_context *ctx;
+                struct trace_entry *entry = record;
+
+                rcu_read_lock();
+                ctx = rcu_dereference(task->perf_event_ctxp[perf_sw_context]);
+                if (!ctx)
+                        goto unlock;
+
+                list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
+                        if (event->attr.type != PERF_TYPE_TRACEPOINT)
+                                continue;
+                        if (event->attr.config != entry->type)
+                                continue;
+                        if (perf_tp_event_match(event, &data, regs))
+                                perf_swevent_event(event, count, &data, regs);
+                }
+unlock:
+                rcu_read_unlock();
+        }
+
         perf_swevent_put_recursion_context(rctx);
 }
 EXPORT_SYMBOL_GPL(perf_tp_event);
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index b0b107f90af..a096c19f2c2 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -101,7 +101,8 @@ __output_copy(struct perf_output_handle *handle,
 }
 
 /* Callchain handling */
-extern struct perf_callchain_entry *perf_callchain(struct pt_regs *regs);
+extern struct perf_callchain_entry *
+perf_callchain(struct perf_event *event, struct pt_regs *regs);
 extern int get_callchain_buffers(void);
 extern void put_callchain_buffers(void);