From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1427920AbcBSLwy (ORCPT ); Fri, 19 Feb 2016 06:52:54 -0500 Received: from szxga01-in.huawei.com ([58.251.152.64]:19315 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030336AbcBSLww (ORCPT ); Fri, 19 Feb 2016 06:52:52 -0500 From: Wang Nan To: Alexei Starovoitov , Arnaldo Carvalho de Melo , Arnaldo Carvalho de Melo , Brendan Gregg CC: Adrian Hunter , Cody P Schafer , "David S. Miller" , He Kuang , =?UTF-8?q?J=C3=A9r=C3=A9mie=20Galarneau?= , Jiri Olsa , Kirill Smelkov , Li Zefan , Masami Hiramatsu , Namhyung Kim , Peter Zijlstra , , Wang Nan , Subject: [PATCH 52/55] perf record: Rename variable to make code clear Date: Fri, 19 Feb 2016 11:44:40 +0000 Message-ID: <1455882283-79592-53-git-send-email-wangnan0@huawei.com> X-Mailer: git-send-email 1.8.3.4 In-Reply-To: <1455882283-79592-1-git-send-email-wangnan0@huawei.com> References: <1455882283-79592-1-git-send-email-wangnan0@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.107.193.248] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090202.56C7007C.0046,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 460df08315c2069f762896d6a977268b Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org record__mmap_read() write data from ring buffer into perf.data. 'head' is maintained by kernel, points to the last writtend 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 naming of variables are not easy to read. 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 Signed-off-by: He Kuang Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Masami Hiramatsu Cc: Namhyung Kim Cc: Zefan Li Cc: pi3orama@163.com --- tools/perf/builtin-record.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index e39475b..b1f37f0 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -91,17 +91,18 @@ static int record__mmap_read(struct record *rec, int idx) 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"); @@ -110,10 +111,10 @@ static int record__mmap_read(struct record *rec, int idx) 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; @@ -121,16 +122,16 @@ static int record__mmap_read(struct record *rec, int idx) } } - 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; -- 1.8.3.4