On Tue, Dec 17, 2019 at 5:00 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > On 12/16/19 6:59 PM, Andrii Nakryiko wrote: > > On Mon, Dec 16, 2019 at 6:44 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > >> On Wed, Dec 11, 2019 at 05:35:20PM -0800, Andrii Nakryiko wrote: > >>> This patch set fixes perf_buffer__new() behavior on systems which have some of > >>> the CPUs offline/missing (due to difference between "possible" and "online" > >>> sets). perf_buffer will create per-CPU buffer and open/attach to corresponding > >>> perf_event only on CPUs present and online at the moment of perf_buffer > >>> creation. Without this logic, perf_buffer creation has no chances of > >>> succeeding on such systems, preventing valid and correct BPF applications from > >>> starting. > >> > >> Once CPU goes back online and processes BPF events, any attempt to push into > >> perf RB via bpf_perf_event_output() with flag BPF_F_CURRENT_CPU would silently > > > > bpf_perf_event_output() will return error code in such case, so it's > > not exactly undetectable by application. > > Yeah, true, given there would be no element in the perf map at that slot, the > program would receive -ENOENT and we could account for missed events via per > CPU map or such. > > >> get discarded. Should rather perf API be fixed instead of plain skipping as done > >> here to at least allow creation of ring buffer for BPF to avoid such case? > > > > Can you elaborate on what perf API fix you have in mind? Do you mean > > for perf to allow attaching ring buffer to offline CPU or something > > else? > > Yes, was wondering about the former, meaning, possibility to attach ring buffer > to offline CPU. This sounds like a more heavy-weight fix, I'll put it on backburner for now and will look at perf code when I get a chance to see if/how it's possible. > > >>> Andrii Nakryiko (4): > >>> libbpf: extract and generalize CPU mask parsing logic > >>> selftests/bpf: add CPU mask parsing tests > >>> libbpf: don't attach perf_buffer to offline/missing CPUs > >>> selftests/bpf: fix perf_buffer test on systems w/ offline CPUs > >>> > >>> tools/lib/bpf/libbpf.c | 157 ++++++++++++------ > >>> tools/lib/bpf/libbpf_internal.h | 2 + > >>> .../selftests/bpf/prog_tests/cpu_mask.c | 78 +++++++++ > >>> .../selftests/bpf/prog_tests/perf_buffer.c | 29 +++- > >>> 4 files changed, 213 insertions(+), 53 deletions(-) > >>> create mode 100644 tools/testing/selftests/bpf/prog_tests/cpu_mask.c > >>> > >>> -- > >>> 2.17.1 > >>> >
