Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH] perf-stat: introduce bperf, share hardware PMCs with BPF | Date | Fri, 12 Mar 2021 16:09:53 +0000 |
| |
> On Mar 12, 2021, at 7:45 AM, Song Liu <songliubraving@fb.com> wrote: > > > >> On Mar 12, 2021, at 4:12 AM, Jiri Olsa <jolsa@redhat.com> wrote: >> >> On Thu, Mar 11, 2021 at 06:02:57PM -0800, Song Liu wrote: >>> perf uses performance monitoring counters (PMCs) to monitor system >>> performance. The PMCs are limited hardware resources. For example, >>> Intel CPUs have 3x fixed PMCs and 4x programmable PMCs per cpu. >>> >>> Modern data center systems use these PMCs in many different ways: >>> system level monitoring, (maybe nested) container level monitoring, per >>> process monitoring, profiling (in sample mode), etc. In some cases, >>> there are more active perf_events than available hardware PMCs. To allow >>> all perf_events to have a chance to run, it is necessary to do expensive >>> time multiplexing of events. >>> >>> On the other hand, many monitoring tools count the common metrics (cycles, >>> instructions). It is a waste to have multiple tools create multiple >>> perf_events of "cycles" and occupy multiple PMCs. >>> >>> bperf tries to reduce such wastes by allowing multiple perf_events of >>> "cycles" or "instructions" (at different scopes) to share PMUs. Instead >>> of having each perf-stat session to read its own perf_events, bperf uses >>> BPF programs to read the perf_events and aggregate readings to BPF maps. >>> Then, the perf-stat session(s) reads the values from these BPF maps. >>> >>> Please refer to the comment before the definition of bperf_ops for the >>> description of bperf architecture. >>> >>> bperf is off by default. To enable it, pass --use-bpf option to perf-stat. >>> bperf uses a BPF hashmap to share information about BPF programs and maps >>> used by bperf. This map is pinned to bpffs. The default address is >>> /sys/fs/bpf/bperf_attr_map. The user could change the address with option >>> --attr-map. >> >> nice, I recall the presentation about that and was wondering >> when this will come up ;-) > > The progress is slower than I expected. But I finished some dependencies of > this in the last year: > > 1. BPF_PROG_TEST_RUN for raw_tp event; > 2. perf-stat -b, which introduced skeleton and bpf_counter; > 3. BPF task local storage, I didn't use it in this version, but it could, > help optimize bperf in the future. > >> >>> >>> --- >>> Known limitations: >>> 1. Do not support per cgroup events; >>> 2. Do not support monitoring of BPF program (perf-stat -b); >>> 3. Do not support event groups. >>> >>> The following commands have been tested: >>> >>> perf stat --use-bpf -e cycles -a >>> perf stat --use-bpf -e cycles -C 1,3,4 >>> perf stat --use-bpf -e cycles -p 123 >>> perf stat --use-bpf -e cycles -t 100,101 >> >> I assume the output is same as standard perf?
Btw, please give it a try. :)
It worked pretty well in my tests. If it doesn't work for some combination of options, please let me know.
Thanks, Song
> > Yes, the output is identical to that without --use-bpf option.
| |