linux-kernel - [PATCH] perf mmap: Discard head in overwrite_rb_find

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Date:   Tue, 6 Mar 2018 19:44:23 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     <acme@...hat.com>
CC:     <mingo@...hat.com>, <peterz@...radead.org>, <namhyung@...nel.org>,
        <jolsa@...hat.com>, <alexander.shishkin@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>,
        Yisheng Xie <xieyisheng1@...wei.com>
Subject: [PATCH] perf mmap: Discard head in overwrite_rb_find_range

In overwrite mode, start will be set to head in perf_mmap__read_init.
Therefore, it is no need to set the start one more in
overwrite_rb_find_range and *start can be used as head instead of
passing head to overwrite_rb_find_range.

Signed-off-by: Yisheng Xie <xieyisheng1@...wei.com>
---
 tools/perf/util/mmap.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
index 91531a7..6751ac9 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -223,19 +223,18 @@ int perf_mmap__mmap(struct perf_mmap *map, struct mmap_params *mp, int fd)
 	return 0;
 }
 
-static int overwrite_rb_find_range(void *buf, int mask, u64 head, u64 *start, u64 *end)
+static int overwrite_rb_find_range(void *buf, int mask, u64 *start, u64 *end)
 {
 	struct perf_event_header *pheader;
-	u64 evt_head = head;
+	u64 evt_head = *start;
 	int size = mask + 1;
 
-	pr_debug2("overwrite_rb_find_range: buf=%p, head=%"PRIx64"\n", buf, head);
-	pheader = (struct perf_event_header *)(buf + (head & mask));
-	*start = head;
+	pr_debug2("%s: buf=%p, start=%"PRIx64"\n", __func__, buf, *start);
+	pheader = (struct perf_event_header *)(buf + (*start & mask));
 	while (true) {
-		if (evt_head - head >= (unsigned int)size) {
+		if (evt_head - *start >= (unsigned int)size) {
 			pr_debug("Finished reading overwrite ring buffer: rewind\n");
-			if (evt_head - head > (unsigned int)size)
+			if (evt_head - *start > (unsigned int)size)
 				evt_head -= pheader->size;
 			*end = evt_head;
 			return 0;
@@ -287,7 +286,7 @@ int perf_mmap__read_init(struct perf_mmap *md, bool overwrite,
 		 * Backward ring buffer is full. We still have a chance to read
 		 * most of data from it.
 		 */
-		if (overwrite_rb_find_range(data, md->mask, head, startp, endp))
+		if (overwrite_rb_find_range(data, md->mask, startp, endp))
 			return -EINVAL;
 	}
 
-- 
1.7.12.4