perf tools: Start the perf.data mapping at data offset in perf trace

Currently, we are mapping perf.data in the beginning of the file
and use the data offset as a buffer offset.

This may exceed the mapping area if the data offset is upper than
page_size * mmap_window and result in a page fault (thing that
happen if we merge trace.info in perf.data).

Instead, let's start the mapping in the page that matches our data
offset.

v2: Drop a junk from another patch (trace_report() removal)

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <1254856886-10348-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 1 deletions

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 5d4c84d86373..d573d4ea6c21 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -143,6 +143,7 @@ static int __cmd_trace(void)
         int ret, rc = EXIT_FAILURE;
         unsigned long offset = 0;
         unsigned long head = 0;
+        unsigned long shift;
         struct stat perf_stat;
         event_t *event;
         uint32_t size;
@@ -180,6 +181,10 @@ static int __cmd_trace(void)
                 return EXIT_FAILURE;
         }
 
+        shift = page_size * (head / page_size);
+        offset += shift;
+        head -= shift;
+
 remap:
         buf = (char *)mmap(NULL, page_size * mmap_window, PROT_READ,
                            MAP_SHARED, input, offset);
@@ -192,9 +197,9 @@ more:
         event = (event_t *)(buf + head);
 
         if (head + event->header.size >= page_size * mmap_window) {
-                unsigned long shift = page_size * (head / page_size);
                 int res;
 
+                shift = page_size * (head / page_size);
                 res = munmap(buf, page_size * mmap_window);
                 assert(res == 0);