Re: [PATCH] perf-stat: introduce bperf, share hardware PMCs with BPF

[Jiri Olsa <jolsa@redhat.com>]

On Fri, Mar 12, 2021 at 04:09:53PM +0000, Song Liu wrote:
> 
> 
> > 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. 

heya, can't compile

  CLANG    /home/jolsa/linux-perf/tools/perf/util/bpf_skel/.tmp/bperf_follower.bpf.o
util/bpf_skel/bperf_follower.bpf.c:8:10: fatal error: 'bperf_u.h' file not found
#include "bperf_u.h"
         ^~~~~~~~~~~

jirka