perf_counter tools: Handle lost events
Make use of the new ->data_tail mechanism to tell kernel-space
about user-space draining the data stream. Emit lost events
(and display them) if they happen.
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/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index e1dfef2..06fdfb8 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -78,10 +78,10 @@
static struct mmap_data mmap_array[MAX_NR_CPUS][MAX_COUNTERS];
-static unsigned int mmap_read_head(struct mmap_data *md)
+static unsigned long mmap_read_head(struct mmap_data *md)
{
struct perf_counter_mmap_page *pc = md->base;
- int head;
+ long head;
head = pc->data_head;
rmb();
@@ -89,6 +89,17 @@
return head;
}
+static void mmap_write_tail(struct mmap_data *md, unsigned long tail)
+{
+ struct perf_counter_mmap_page *pc = md->base;
+
+ /*
+ * ensure all reads are done before we write the tail out.
+ */
+ /* mb(); */
+ pc->data_tail = tail;
+}
+
static void mmap_read(struct mmap_data *md)
{
unsigned int head = mmap_read_head(md);
@@ -109,7 +120,7 @@
* In either case, truncate and restart at head.
*/
diff = head - old;
- if (diff > md->mask / 2 || diff < 0) {
+ if (diff < 0) {
struct timeval iv;
unsigned long msecs;
@@ -167,6 +178,7 @@
}
md->prev = old;
+ mmap_write_tail(md, old);
}
static volatile int done = 0;
@@ -424,7 +436,7 @@
mmap_array[nr_cpu][counter].prev = 0;
mmap_array[nr_cpu][counter].mask = mmap_pages*page_size - 1;
mmap_array[nr_cpu][counter].base = mmap(NULL, (mmap_pages+1)*page_size,
- PROT_READ, MAP_SHARED, fd[nr_cpu][counter], 0);
+ PROT_READ|PROT_WRITE, MAP_SHARED, fd[nr_cpu][counter], 0);
if (mmap_array[nr_cpu][counter].base == MAP_FAILED) {
error("failed to mmap with %d (%s)\n", errno, strerror(errno));
exit(-1);