libperf evlist: Fix polling of system-wide events

Originally, (refer commit f90d194a867a5a1d ("perf evlist: Do not poll
events that use the system_wide flag") there wasn't much reason to poll
system-wide events because:

1. The mmaps get "merged" via set-output anyway (the per-cpu case)
2. perf reads all mmaps when any event is woken
3. system-wide mmaps do not fill up as fast as the mmaps for user
selected events

But there was 1 reason not to poll which was that it prevented correct
termination due to POLLHUP on all user selected events. That issue is
now easily resolved by using fdarray_flag__nonfilterable.

With the advent of commit ae4f8ae16a078964 ("libperf evlist: Allow
mixing per-thread and per-cpu mmaps"), system-wide mmaps can be used
also in the per-thread case where reason 1 does not apply.

Fix the omission of system-wide events from polling by using the
fdarray_flag__nonfilterable flag.

Example:

Before:

$ perf record --no-bpf-event -vvv -e intel_pt// --per-thread uname 2>err.txt
Linux
$ grep 'sys_perf_event_open.*=\|pollfd' err.txt
sys_perf_event_open: pid 155076 cpu -1 group_fd -1 flags 0x8 = 5
sys_perf_event_open: pid 155076 cpu -1 group_fd -1 flags 0x8 = 6
sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 7
sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 9
sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8 = 10
sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8 = 11
sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8 = 12
sys_perf_event_open: pid -1 cpu 5 group_fd -1 flags 0x8 = 13
sys_perf_event_open: pid -1 cpu 6 group_fd -1 flags 0x8 = 14
sys_perf_event_open: pid -1 cpu 7 group_fd -1 flags 0x8 = 15
thread_data[0x55fb43c29e80]: pollfd[0] <- event_fd=5
thread_data[0x55fb43c29e80]: pollfd[1] <- event_fd=6
thread_data[0x55fb43c29e80]: pollfd[2] <- non_perf_event fd=4

After:

$ perf record --no-bpf-event -vvv -e intel_pt// --per-thread uname 2>err.txt
Linux
$ grep 'sys_perf_event_open.*=\|pollfd' err.txt
sys_perf_event_open: pid 156316 cpu -1 group_fd -1 flags 0x8 = 5
sys_perf_event_open: pid 156316 cpu -1 group_fd -1 flags 0x8 = 6
sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 7
sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 9
sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8 = 10
sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8 = 11
sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8 = 12
sys_perf_event_open: pid -1 cpu 5 group_fd -1 flags 0x8 = 13
sys_perf_event_open: pid -1 cpu 6 group_fd -1 flags 0x8 = 14
sys_perf_event_open: pid -1 cpu 7 group_fd -1 flags 0x8 = 15
thread_data[0x55cc19e58e80]: pollfd[0] <- event_fd=5
thread_data[0x55cc19e58e80]: pollfd[1] <- event_fd=6
thread_data[0x55cc19e58e80]: pollfd[2] <- event_fd=7
thread_data[0x55cc19e58e80]: pollfd[3] <- event_fd=9
thread_data[0x55cc19e58e80]: pollfd[4] <- event_fd=10
thread_data[0x55cc19e58e80]: pollfd[5] <- event_fd=11
thread_data[0x55cc19e58e80]: pollfd[6] <- event_fd=12
thread_data[0x55cc19e58e80]: pollfd[7] <- event_fd=13
thread_data[0x55cc19e58e80]: pollfd[8] <- event_fd=14
thread_data[0x55cc19e58e80]: pollfd[9] <- event_fd=15
thread_data[0x55cc19e58e80]: pollfd[10] <- non_perf_event fd=4

Fixes: ae4f8ae16a078964 ("libperf evlist: Allow mixing per-thread and per-cpu mmaps")
Signed-off-by: Adrian Hunter <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/perf/evlist.c

···
 
 	perf_evlist__for_each_entry(evlist, evsel) {
 		bool overwrite = evsel->attr.write_backward;
+		enum fdarray_flags flgs;
 		struct perf_mmap *map;
 		int *output, fd, cpu;
 
···
 
 		revent = !overwrite ? POLLIN : 0;
 
-		if (!evsel->system_wide &&
-		    perf_evlist__add_pollfd(evlist, fd, map, revent, fdarray_flag__default) < 0) {
+		flgs = evsel->system_wide ? fdarray_flag__nonfilterable : fdarray_flag__default;
+		if (perf_evlist__add_pollfd(evlist, fd, map, revent, flgs) < 0) {
 			perf_mmap__put(map);
 			return -1;
 		}