perf record: Rename variable to make code clear
record__mmap_read() writes data from ring buffer into perf.data. 'head'
is maintained by the kernel, points to the last written record.
'old' is maintained by perf, points to the record read in previous
round. record__mmap_read() saves data from 'old' to 'head' to
perf.data.
The names of these variables are not very intutive. In addition,
when dealing with backward writing ring buffer, the md->prev pointer
should point to 'head' instead of the last byte it got.
Add 'start' and 'end' pointer to make code clear and set md->prev to
'head' instead of the moved 'old' pointer. This patch doesn't change
behavior since:
buf = &data[old & md->mask];
size = head - old;
old += size; <--- Here, old == head
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1463987628-163563-4-git-send-email-wangnan0@huawei.com
Signed-off-by: He Kuang <hekuang@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index f302cc9..73ce651 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -88,17 +88,18 @@
struct perf_mmap *md = &rec->evlist->mmap[idx];
u64 head = perf_mmap__read_head(md);
u64 old = md->prev;
+ u64 end = head, start = old;
unsigned char *data = md->base + page_size;
unsigned long size;
void *buf;
int rc = 0;
- if (old == head)
+ if (start == end)
return 0;
rec->samples++;
- size = head - old;
+ size = end - start;
if (size > (unsigned long)(md->mask) + 1) {
WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");
@@ -107,10 +108,10 @@
return 0;
}
- if ((old & md->mask) + size != (head & md->mask)) {
- buf = &data[old & md->mask];
- size = md->mask + 1 - (old & md->mask);
- old += size;
+ if ((start & md->mask) + size != (end & md->mask)) {
+ buf = &data[start & md->mask];
+ size = md->mask + 1 - (start & md->mask);
+ start += size;
if (record__write(rec, buf, size) < 0) {
rc = -1;
@@ -118,16 +119,16 @@
}
}
- buf = &data[old & md->mask];
- size = head - old;
- old += size;
+ buf = &data[start & md->mask];
+ size = end - start;
+ start += size;
if (record__write(rec, buf, size) < 0) {
rc = -1;
goto out;
}
- md->prev = old;
+ md->prev = head;
perf_evlist__mmap_consume(rec->evlist, idx);
out:
return rc;