perf record: No need to check for overwrites

As we open the mmap with (PROT_READ | PROT_WRITE), signalling the kernel
with perf_mmap__write_tail() when consuming data, so the kernel will not
overwrite.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 3 insertions, 19 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index d7886307f6f4..caf927978d92 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -115,27 +115,11 @@ static void mmap_read(struct perf_mmap *md)
         unsigned char *data = md->base + page_size;
         unsigned long size;
         void *buf;
-        int diff;
 
-        /*
-         * If we're further behind than half the buffer, there's a chance
-         * the writer will bite our tail and mess up the samples under us.
-         *
-         * If we somehow ended up ahead of the head, we got messed up.
-         *
-         * In either case, truncate and restart at head.
-         */
-        diff = head - old;
-        if (diff < 0) {
-                fprintf(stderr, "WARNING: failed to keep up with mmap data\n");
-                /*
-                 * head points to a known good entry, start there.
-                 */
-                old = head;
-        }
+        if (old == head)
+                return;
 
-        if (old != head)
-                samples++;
+        samples++;
 
         size = head - old;