Messages in this thread | | | Subject | Re: [PATCH v15 03/12] perf tools: Update perf evlist mmap related APIs and helpers | From | "Wangnan (F)" <> | Date | Thu, 14 Jul 2016 09:58:09 +0800 |
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On 2016/7/13 22:06, Jiri Olsa wrote: > On Tue, Jul 12, 2016 at 10:00:03AM +0000, Wang Nan wrote: > > SNIP > >> -union perf_event *perf_evlist__mmap_read_forward(struct perf_evlist *evlist, int idx) >> +union perf_event *perf_mmap__read_forward(struct perf_mmap *md, bool overwrite) >> { >> - struct perf_mmap *md = &evlist->mmap[idx]; >> u64 head; >> u64 old = md->prev; >> >> @@ -795,13 +795,12 @@ union perf_event *perf_evlist__mmap_read_forward(struct perf_evlist *evlist, int >> >> head = perf_mmap__read_head(md); >> >> - return perf_mmap__read(md, evlist->overwrite, old, head, &md->prev); >> + return perf_mmap__read(md, overwrite, old, head, &md->prev); >> } >> >> union perf_event * >> -perf_evlist__mmap_read_backward(struct perf_evlist *evlist, int idx) >> +perf_mmap__read_backward(struct perf_mmap *md, bool overwrite __maybe_unused) >> { >> - struct perf_mmap *md = &evlist->mmap[idx]; >> u64 head, end; >> u64 start = md->prev; >> >> @@ -836,6 +835,20 @@ perf_evlist__mmap_read_backward(struct perf_evlist *evlist, int idx) >> return perf_mmap__read(md, false, start, end, &md->prev); > should you pas evlist->overwrite in here?
No need. The second arg of perf_mmap__read() is not 'overwrite', but 'check_messup'. When set to 'true', stop reading if caller require a buffer larger than half of the size of the ring buffer and report a warning. Only forward, read-only ring buffer requires this check. We can always read the whole backward ring buffer because we pause it before reading.
I'll add more comments here.
Thank you.
> thanks, > jirka
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