On 2017/11/1 20:39, Jiri Olsa wrote:
On Wed, Nov 01, 2017 at 08:10:49PM +0800, Wangnan (F) wrote: SNIPdiff --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. Patch 2/2 clarifies these concepts. What we want is the flight recorder mode, not only a read only ring buffer. Even flight recorder mode is selected, we can still have a normal ring buffer which keep output data. Thank you.
