linux-kernel - [tip:perf/core] perf record: No need to check for overwrites

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Date:	Mon, 31 Jan 2011 12:48:45 GMT
From:	tip-bot for Arnaldo Carvalho de Melo <acme@...hat.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, eranian@...gle.com, paulus@...ba.org,
	acme@...hat.com, hpa@...or.com, mingo@...hat.com,
	tzanussi@...il.com, efault@....de, peterz@...radead.org,
	fweisbec@...il.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:perf/core] perf record: No need to check for overwrites

Commit-ID:  dc82009aac6ee6e423b48de43a251745c62ab012
Gitweb:     http://git.kernel.org/tip/dc82009aac6ee6e423b48de43a251745c62ab012
Author:     Arnaldo Carvalho de Melo <acme@...hat.com>
AuthorDate: Fri, 28 Jan 2011 14:49:19 -0200
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Sat, 29 Jan 2011 16:23:58 -0200

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@...radead.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Mike Galbraith <efault@....de>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Tom Zanussi <tzanussi@...il.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/builtin-record.c |   24 ++++--------------------
 1 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index d788630..caf9279 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;
 
--
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