Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752165AbcDZCb7 (ORCPT ); Mon, 25 Apr 2016 22:31:59 -0400 Received: from szxga02-in.huawei.com ([119.145.14.65]:38673 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751322AbcDZCbV (ORCPT ); Mon, 25 Apr 2016 22:31:21 -0400 From: Wang Nan To: CC: , Wang Nan , "Arnaldo Carvalho de Melo" , Peter Zijlstra , Zefan Li , Subject: [PATCH 3/5] perf tools: Rename variable in __perf_evlist__mmap_read() Date: Tue, 26 Apr 2016 02:28:56 +0000 Message-ID: <1461637738-62722-4-git-send-email-wangnan0@huawei.com> X-Mailer: git-send-email 1.8.3.4 In-Reply-To: <1461637738-62722-1-git-send-email-wangnan0@huawei.com> References: <1461637738-62722-1-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=0001.0A020203.571ED295.0098,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: 5815ff08474f04827fc6856cf12c0b8b Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3812 Lines: 113 In __perf_evlist__mmap_read(), give better names to pointers. Origianl name 'old' and 'head' directly related to pointers in ring buffer control page. For backward ring buffer, the meaning of 'head' point is not 'the first byte of free space', but 'the first byte of the last record'. To reduce confusion, rename 'old' to 'start', 'head' to 'end'. 'start' -> 'end' is the records should be read from. Change parameter order. Change 'overwrite' to 'check_messup'. When reading from 'head', no need to check messup for for backward ring buffer. Signed-off-by: Wang Nan Cc: Arnaldo Carvalho de Melo Cc: Peter Zijlstra Cc: Zefan Li Cc: pi3orama@163.com --- tools/perf/util/evlist.c | 31 ++++++++++++++++--------------- 1 file changed, 16 insertions(+), 15 deletions(-) diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 3ee94b2..f680983 100644 --- a/tools/perf/util/evlist.c +++ b/tools/perf/util/evlist.c @@ -679,30 +679,31 @@ static struct perf_evsel *perf_evlist__event2evsel(struct perf_evlist *evlist, return NULL; } +/* When check_messup is true, 'end' must points to a known good entry */ static union perf_event * -__perf_evlist__mmap_read(struct perf_mmap *md, bool overwrite, u64 head, - u64 old, u64 *prev) +__perf_evlist__mmap_read(struct perf_mmap *md, bool check_messup, u64 start, + u64 end, u64 *prev) { unsigned char *data = md->base + page_size; union perf_event *event = NULL; - int diff = head - old; + int diff = end - start; - if (overwrite) { + if (check_messup) { /* * 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. + * If we somehow ended up ahead of the 'end', we got messed up. * - * In either case, truncate and restart at head. + * In either case, truncate and restart at 'end'. */ if (diff > md->mask / 2 || diff < 0) { fprintf(stderr, "WARNING: failed to keep up with mmap data.\n"); /* - * head points to a known good entry, start there. + * 'end' points to a known good entry, start there. */ - old = head; + start = end; diff = 0; } } @@ -710,7 +711,7 @@ __perf_evlist__mmap_read(struct perf_mmap *md, bool overwrite, u64 head, if (diff >= (int)sizeof(event->header)) { size_t size; - event = (union perf_event *)&data[old & md->mask]; + event = (union perf_event *)&data[start & md->mask]; size = event->header.size; if (size < sizeof(event->header) || diff < (int)size) { @@ -722,8 +723,8 @@ __perf_evlist__mmap_read(struct perf_mmap *md, bool overwrite, u64 head, * Event straddles the mmap boundary -- header should always * be inside due to u64 alignment of output. */ - if ((old & md->mask) + size != ((old + size) & md->mask)) { - unsigned int offset = old; + if ((start & md->mask) + size != ((start + size) & md->mask)) { + unsigned int offset = start; unsigned int len = min(sizeof(*event), size), cpy; void *dst = md->event_copy; @@ -738,12 +739,12 @@ __perf_evlist__mmap_read(struct perf_mmap *md, bool overwrite, u64 head, event = (union perf_event *) md->event_copy; } - old += size; + start += size; } broken_event: if (prev) - *prev = old; + *prev = start; return event; } @@ -762,8 +763,8 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx) head = perf_mmap__read_head(md); - return __perf_evlist__mmap_read(md, evlist->overwrite, head, - old, &md->prev); + return __perf_evlist__mmap_read(md, evlist->overwrite, old, + head, &md->prev); } static bool perf_mmap__empty(struct perf_mmap *md) -- 1.8.3.4