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Date: Wed, 1 Nov 2017 13:39:57 +0100 From: Jiri Olsa <jolsa@...hat.com> To: "Wangnan (F)" <wangnan0@...wei.com> Cc: Namhyung Kim <namhyung@...nel.org>, linux-kernel@...r.kernel.org, kan.liang@...el.com, acme@...nel.org, kernel-team@....com Subject: Re: [PATCH 1/2] perf mmap: Fix perf backward recording On Wed, Nov 01, 2017 at 08:10:49PM +0800, Wangnan (F) wrote: SNIP > > > > diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c > > > > index c6c891e154a6..27ebe355e794 100644 > > > > --- a/tools/perf/util/evlist.c > > > > +++ b/tools/perf/util/evlist.c > > > > @@ -838,6 +838,11 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx, > > > > if (*output == -1) { > > > > *output = fd; > > > > + if (evsel->attr.write_backward) > > > > + mp->prot = PROT_READ; > > > > + else > > > > + mp->prot = PROT_READ | PROT_WRITE; > > > > + > > > If evlist->overwrite is true, PROT_WRITE should be unset even if > > > write_backward is > > > not set. If you want to delay the setting of mp->prot, you need to consider > > > both evlist->overwrite and evsel->attr.write_backward. > > I thought evsel->attr.write_backward should be set when > > evlist->overwrite is set. Do you mean following case? > > > > perf record --overwrite -e 'cycles/no-overwrite/' > > > > No. evlist->overwrite is unrelated to '--overwrite'. This is why I > said the concept of 'overwrite' and 'backward' is ambiguous. > > perf record never sets 'evlist->overwrite'. What '--overwrite' actually > does is setting write_backward. Some testcases needs overwrite evlist. did not check deeply, but so why can't we do the below? jirka --- diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index f4d9fc54b382..4643c487bd29 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -300,7 +300,7 @@ static int record__mmap_evlist(struct record *rec, struct record_opts *opts = &rec->opts; char msg[512]; - if (perf_evlist__mmap_ex(evlist, opts->mmap_pages, false, + if (perf_evlist__mmap_ex(evlist, opts->mmap_pages, opts->overwrite, opts->auxtrace_mmap_pages, opts->auxtrace_snapshot_mode) < 0) { if (errno == EPERM) {
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