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>

1 files changed, 16 insertions, 4 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index e1dfef24887f..06fdfb8b4828 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -78,10 +78,10 @@ struct mmap_data {
 
 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 @@ static unsigned int mmap_read_head(struct mmap_data *md)
         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 @@ static void mmap_read(struct mmap_data *md)
          * 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 @@ static void mmap_read(struct mmap_data *md)
         }
 
         md->prev = old;
+        mmap_write_tail(md, old);
 }
 
 static volatile int done = 0;
@@ -424,7 +436,7 @@ try_again:
         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);