From b6b85dad30ad7e7394990e2317a780577974a4e6 Mon Sep 17 00:00:00 2001 From: Wang Nan Date: Wed, 27 Apr 2016 02:19:21 +0000 Subject: perf evlist: Rename variable in perf_mmap__read() In perf_mmap__read(), give better names to pointers. Original 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 direction 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: Peter Zijlstra Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1461723563-67451-3-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/evlist.c | 29 +++++++++++++++-------------- 1 file changed, 15 insertions(+), 14 deletions(-) (limited to 'tools/perf/util') diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 96c71916e367..17cd01421e7f 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 good entry */ static union perf_event * -perf_mmap__read(struct perf_mmap *md, bool overwrite, u64 head, - u64 old, u64 *prev) +perf_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_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_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_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; } @@ -762,7 +763,7 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx) head = perf_mmap__read_head(md); - return perf_mmap__read(md, evlist->overwrite, head, old, &md->prev); + return perf_mmap__read(md, evlist->overwrite, old, head, &md->prev); } static bool perf_mmap__empty(struct perf_mmap *md) -- cgit v1.2.3