From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754701AbcBEOLu (ORCPT ); Fri, 5 Feb 2016 09:11:50 -0500 Received: from szxga03-in.huawei.com ([119.145.14.66]:11461 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754270AbcBEOFF (ORCPT ); Fri, 5 Feb 2016 09:05:05 -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 51/54] perf record: Rename variable to make code clear Date: Fri, 5 Feb 2016 14:02:16 +0000 Message-ID: <1454680939-24963-52-git-send-email-wangnan0@huawei.com> X-Mailer: git-send-email 1.8.3.4 In-Reply-To: <1454680939-24963-1-git-send-email-wangnan0@huawei.com> References: <1454680939-24963-1-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=0001.0A020203.56B4ABC6.02BB,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-05-26 15:14:31, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 2ee963d7a94a82f0c13f7780a99491ff 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 4d89543..b4f0c61 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