Commit 38b200d6 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf_counter: Add PERF_EVENT_READ 



Provide a read() like event which can be used to log the
counter value at specific sites such as child->parent
folding on exit.

In order to be useful, we log the counter parent ID, not the
actual counter ID, since userspace can only relate parent
IDs to perf_counter_attr constructs.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 194002b2

include/linux/perf_counter.h

+12 −0
Original line number Diff line number Diff line
@@ -334,6 +334,18 @@ enum perf_event_type { 
	 */

	PERF_EVENT_FORK			= 7,



	/*

	 * struct {

	 * 	struct perf_event_header	header;

	 * 	u32				pid, tid;

	 * 	u64				value;

	 * 	{ u64		time_enabled; 	} && PERF_FORMAT_ENABLED

	 * 	{ u64		time_running; 	} && PERF_FORMAT_RUNNING

	 * 	{ u64		parent_id;	} && PERF_FORMAT_ID

	 * };

	 */

	PERF_EVENT_READ			= 8,



	/*

	 * When header.misc & PERF_EVENT_MISC_OVERFLOW the event_type field

	 * will be PERF_SAMPLE_*

kernel/perf_counter.c

+68 −4
Original line number Diff line number Diff line
@@ -2623,6 +2623,66 @@ static void perf_counter_output(struct perf_counter *counter, int nmi, 
	perf_output_end(&handle);

}



/*

 * read event

 */



struct perf_read_event {

	struct perf_event_header	header;



	u32				pid;

	u32				tid;

	u64				value;

	u64				format[3];

};



static void

perf_counter_read_event(struct perf_counter *counter,

			struct task_struct *task)

{

	struct perf_output_handle handle;

	struct perf_read_event event = {

		.header = {

			.type = PERF_EVENT_READ,

			.misc = 0,

			.size = sizeof(event) - sizeof(event.format),

		},

		.pid = perf_counter_pid(counter, task),

		.tid = perf_counter_tid(counter, task),

		.value = atomic64_read(&counter->count),

	};

	int ret, i = 0;



	if (counter->attr.read_format & PERF_FORMAT_TOTAL_TIME_ENABLED) {

		event.header.size += sizeof(u64);

		event.format[i++] = counter->total_time_enabled;

	}



	if (counter->attr.read_format & PERF_FORMAT_TOTAL_TIME_RUNNING) {

		event.header.size += sizeof(u64);

		event.format[i++] = counter->total_time_running;

	}



	if (counter->attr.read_format & PERF_FORMAT_ID) {

		u64 id;



		event.header.size += sizeof(u64);

		if (counter->parent)

			id = counter->parent->id;

		else

			id = counter->id;



		event.format[i++] = id;

	}



	ret = perf_output_begin(&handle, counter, event.header.size, 0, 0);

	if (ret)

		return;



	perf_output_copy(&handle, &event, event.header.size);

	perf_output_end(&handle);

}



/*

 * fork tracking

 */
@@ -3985,10 +4045,13 @@ static int inherit_group(struct perf_counter *parent_counter, 
}



static void sync_child_counter(struct perf_counter *child_counter,

			       struct perf_counter *parent_counter)

			       struct task_struct *child)

{

	struct perf_counter *parent_counter = child_counter->parent;

	u64 child_val;



	perf_counter_read_event(child_counter, child);



	child_val = atomic64_read(&child_counter->count);



	/*
@@ -4017,7 +4080,8 @@ static void sync_child_counter(struct perf_counter *child_counter, 


static void

__perf_counter_exit_task(struct perf_counter *child_counter,

			 struct perf_counter_context *child_ctx)

			 struct perf_counter_context *child_ctx,

			 struct task_struct *child)

{

	struct perf_counter *parent_counter;
@@ -4031,7 +4095,7 @@ __perf_counter_exit_task(struct perf_counter *child_counter, 
	 * counters need to be zapped - but otherwise linger.

	 */

	if (parent_counter) {

		sync_child_counter(child_counter, parent_counter);

		sync_child_counter(child_counter, child);

		free_counter(child_counter);

	}

}
@@ -4093,7 +4157,7 @@ void perf_counter_exit_task(struct task_struct *child) 
again:

	list_for_each_entry_safe(child_counter, tmp, &child_ctx->counter_list,

				 list_entry)

		__perf_counter_exit_task(child_counter, child_ctx);

		__perf_counter_exit_task(child_counter, child_ctx, child);



	/*

	 * If the last counter was a group counter, it will have appended all

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