Messages in this thread | | | Date | Thu, 2 Nov 2017 16:12:08 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH 1/2] perf mmap: Fix perf backward recording |
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On Wed, Nov 01, 2017 at 08:56:32PM +0800, Wangnan (F) wrote: > > > On 2017/11/1 20:39, Jiri Olsa wrote: > > 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) { > > perf_evlist__mmap_ex's overwrite argument is used to control evlist->mmap. > > Consider Namhyung's example: > > perf record --overwrite -e 'cycles/no-overwrite/' > > In this case both evlist->mmap and evlist->backward_mmap would be set to overwrite. > 'cycles' will be put into evlist->mmap, so it will be set to overwrite incorrectly.
right, missed the separate mmaps..
so we have some code that uses evlist->overwrite, which is always set to 'false' in perf record.. but in the crucial checks like for perf_mmap__consume we use the 'backward' bool to save the day
that might need some consolidation as well.. we could keep the overwrite flag in the struct perf_mmap.. that could simplify the code
jirka
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