perf evlist: Support non overwrite mode in perf_evlist__read_on_cpu

I.e. stash the overwrite mode in struct perf_evlist and act accordingly
in perf_evlist__read_on_cpu, not checking for overwrites and touching
the tail after consuming one event, like perf record does, for instance.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -327,6 +327,7 @@ int perf_evlist__mmap(struct perf_evlist *evlist, struct cpu_map *cpus,
 	    perf_evlist__alloc_pollfd(evlist, cpus->nr, threads->nr) < 0)
 		return -ENOMEM;
 
+	evlist->overwrite = overwrite;
 	evlist->mmap_len = (pages + 1) * page_size;
 	first_evsel = list_entry(evlist->entries.next, struct perf_evsel, node);