perf_counter: Add event overlow handling
Alternative method of mmap() data output handling that provides
better overflow management and a more reliable data stream.
Unlike the previous method, that didn't have any user->kernel
feedback and relied on userspace keeping up, this method relies on
userspace writing its last read position into the control page.
It will ensure new output doesn't overwrite not-yet read events,
new events for which there is no space left are lost and the
overflow counter is incremented, providing exact event loss
numbers.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index a7d3a61..0765e8e 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -236,10 +236,16 @@
/*
* Control data for the mmap() data buffer.
*
- * User-space reading this value should issue an rmb(), on SMP capable
- * platforms, after reading this value -- see perf_counter_wakeup().
+ * User-space reading the @data_head value should issue an rmb(), on
+ * SMP capable platforms, after reading this value -- see
+ * perf_counter_wakeup().
+ *
+ * When the mapping is PROT_WRITE the @data_tail value should be
+ * written by userspace to reflect the last read data. In this case
+ * the kernel will not over-write unread data.
*/
__u64 data_head; /* head in the data section */
+ __u64 data_tail; /* user-space written tail */
};
#define PERF_EVENT_MISC_CPUMODE_MASK (3 << 0)
@@ -275,6 +281,15 @@
/*
* struct {
+ * struct perf_event_header header;
+ * u64 id;
+ * u64 lost;
+ * };
+ */
+ PERF_EVENT_LOST = 2,
+
+ /*
+ * struct {
* struct perf_event_header header;
*
* u32 pid, tid;
@@ -313,26 +328,26 @@
/*
* When header.misc & PERF_EVENT_MISC_OVERFLOW the event_type field
- * will be PERF_RECORD_*
+ * will be PERF_SAMPLE_*
*
* struct {
* struct perf_event_header header;
*
- * { u64 ip; } && PERF_RECORD_IP
- * { u32 pid, tid; } && PERF_RECORD_TID
- * { u64 time; } && PERF_RECORD_TIME
- * { u64 addr; } && PERF_RECORD_ADDR
- * { u64 config; } && PERF_RECORD_CONFIG
- * { u32 cpu, res; } && PERF_RECORD_CPU
+ * { u64 ip; } && PERF_SAMPLE_IP
+ * { u32 pid, tid; } && PERF_SAMPLE_TID
+ * { u64 time; } && PERF_SAMPLE_TIME
+ * { u64 addr; } && PERF_SAMPLE_ADDR
+ * { u64 config; } && PERF_SAMPLE_CONFIG
+ * { u32 cpu, res; } && PERF_SAMPLE_CPU
*
* { u64 nr;
- * { u64 id, val; } cnt[nr]; } && PERF_RECORD_GROUP
+ * { u64 id, val; } cnt[nr]; } && PERF_SAMPLE_GROUP
*
* { u16 nr,
* hv,
* kernel,
* user;
- * u64 ips[nr]; } && PERF_RECORD_CALLCHAIN
+ * u64 ips[nr]; } && PERF_SAMPLE_CALLCHAIN
* };
*/
};
@@ -424,6 +439,7 @@
struct perf_mmap_data {
struct rcu_head rcu_head;
int nr_pages; /* nr of data pages */
+ int writable; /* are we writable */
int nr_locked; /* nr pages mlocked */
atomic_t poll; /* POLL_ for wakeups */
@@ -433,8 +449,8 @@
atomic_long_t done_head; /* completed head */
atomic_t lock; /* concurrent writes */
-
atomic_t wakeup; /* needs a wakeup */
+ atomic_t lost; /* nr records lost */
struct perf_counter_mmap_page *user_page;
void *data_pages[0];