Commit e8c6deac authored Jan 14, 2015 by Alexander Shishkin Committed by Ingo Molnar Apr 02, 2015

perf: Add data_{offset,size} to user_page



Currently, the actual perf ring buffer is one page into the mmap area,
following the user page and the userspace follows this convention. This
patch adds data_{offset,size} fields to user_page that can be used by
userspace instead for locating perf data in the mmap area. This is also
helpful when mapping existing or shared buffers if their size is not
known in advance.

Right now, it is made to follow the existing convention that

	data_offset == PAGE_SIZE and
	data_offset + data_size == mmap_size.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kaixu Xia <kaixu.xia@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Robert Richter <rric@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@infradead.org
Cc: adrian.hunter@intel.com
Cc: kan.liang@intel.com
Cc: markus.t.metzger@intel.com
Cc: mathieu.poirier@linaro.org
Link: http://lkml.kernel.org/r/1421237903-181015-2-git-send-email-alexander.shishkin@linux.intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent e1abf2cc

include/uapi/linux/perf_event.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -522,9 +522,14 @@ struct perf_event_mmap_page {
		* In this case the kernel will not over-write unread data.
		*
		* See perf_output_put_handle() for the data ordering.
		*
		* data_{offset,size} indicate the location and size of the perf record
		* buffer within the mmapped area.
		*/
		__u64 data_head; /* head in the data section */
		__u64 data_tail; /* user-space written tail */
		__u64 data_offset; /* where the buffer starts */
		__u64 data_size; /* data buffer size */
		};

		#define PERF_RECORD_MISC_CPUMODE_MASK (7 << 0)

kernel/events/core.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -4105,6 +4105,8 @@ static void perf_event_init_userpage(struct perf_event *event)
		/* Allow new userspace to detect that bit 0 is deprecated */
		userpg->cap_bit0_is_deprecated = 1;
		userpg->size = offsetof(struct perf_event_mmap_page, __reserved);
		userpg->data_offset = PAGE_SIZE;
		userpg->data_size = perf_data_size(rb);

		unlock:
		rcu_read_unlock();

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