Subject: Re: [PATCH v4 bpf-next 0/4] bpftool: introduce prog profile

From: Jiri Olsa <[email-masked]>
Date: Mon, 9 Mar 2020 20:30:26 +0100

On Mon, Mar 09, 2020 at 06:24:22PM +0000, Song Liu wrote:
> 
> 
> > On Mar 9, 2020, at 11:04 AM, Quentin Monnet <[email-masked]> wrote:
> > 
> > 2020-03-04 21:39 UTC+0000 ~ Song Liu <[email-masked]>
> >> 
> >> 
> >>> On Mar 4, 2020, at 1:29 PM, Jiri Olsa <[email-masked]> wrote:
> >>> 
> >>> On Wed, Mar 04, 2020 at 09:16:29PM +0000, Song Liu wrote:
> >>>> 
> >>>> 
> >>>>> On Mar 4, 2020, at 12:41 PM, Jiri Olsa <[email-masked]> wrote:
> >>>>> 
> >>>>> On Wed, Mar 04, 2020 at 08:08:07PM +0100, Jiri Olsa wrote:
> >>>>>> On Wed, Mar 04, 2020 at 10:07:06AM -0800, Song Liu wrote:
> >>>>>>> This set introduces bpftool prog profile command, which uses hardware
> >>>>>>> counters to profile BPF programs.
> >>>>>>> 
> >>>>>>> This command attaches fentry/fexit programs to a target program. These two
> >>>>>>> programs read hardware counters before and after the target program and
> >>>>>>> calculate the difference.
> >>>>>>> 
> >>>>>>> Changes v3 => v4:
> >>>>>>> 1. Simplify err handling in profile_open_perf_events() (Quentin);
> >>>>>>> 2. Remove redundant p_err() (Quentin);
> >>>>>>> 3. Replace tab with space in bash-completion; (Quentin);
> >>>>>>> 4. Fix typo _bpftool_get_map_names => _bpftool_get_prog_names (Quentin).
> >>>>>> 
> >>>>>> hum, I'm getting:
> >>>>>> 
> >>>>>> 	[jolsa@dell-r440-01 bpftool]$ pwd
> >>>>>> 	/home/jolsa/linux-perf/tools/bpf/bpftool
> >>>>>> 	[jolsa@dell-r440-01 bpftool]$ make
> >>>>>> 	...
> >>>>>> 	make[1]: Leaving directory '/home/jolsa/linux-perf/tools/lib/bpf'
> >>>>>> 	  LINK     _bpftool
> >>>>>> 	make: *** No rule to make target 'skeleton/profiler.bpf.c', needed by 'skeleton/profiler.bpf.o'.  Stop.
> >>>>> 
> >>>>> ok, I had to apply your patches by hand, because 'git am' refused to
> >>>>> due to fuzz.. so some of you new files did not make it to my tree ;-)
> >>>>> 
> >>>>> anyway I hit another error now:
> >>>>> 
> >>>>> 	  CC       prog.o
> >>>>> 	In file included from prog.c:1553:
> >>>>> 	profiler.skel.h: In function ‘profiler_bpf__create_skeleton’:
> >>>>> 	profiler.skel.h:136:35: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>>>> 	  136 |  s->maps[4].mmaped = (void **)&obj->rodata;
> >>>>> 	      |                                   ^~
> >>>>> 	prog.c: In function ‘profile_read_values’:
> >>>>> 	prog.c:1650:29: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>>>> 	 1650 |  __u32 m, cpu, num_cpu = obj->rodata->num_cpu;
> >>>>> 
> >>>>> I'll try to figure it out.. might be error on my end
> >>>>> 
> >>>>> do you have git repo with these changes?
> >>>> 
> >>>> I pushed it to 
> >>>> 
> >>>> https://git.kernel.org/pub/scm/linux/kernel/git/song/linux.git/tree/?h=bpf-per-prog-stats
> >>> 
> >>> still the same:
> >>> 
> >>> 	[jolsa@dell-r440-01 bpftool]$ git show --oneline HEAD | head -1
> >>> 	7bbda5cca00a bpftool: fix typo in bash-completion
> >>> 	[jolsa@dell-r440-01 bpftool]$ make 
> >>> 	make[1]: Entering directory '/home/jolsa/linux-perf/tools/lib/bpf'
> >>> 	make[1]: Leaving directory '/home/jolsa/linux-perf/tools/lib/bpf'
> >>> 	  CC       prog.o
> >>> 	In file included from prog.c:1553:
> >>> 	profiler.skel.h: In function ‘profiler_bpf__create_skeleton’:
> >>> 	profiler.skel.h:136:35: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>> 	  136 |  s->maps[4].mmaped = (void **)&obj->rodata;
> >>> 	      |                                   ^~
> >>> 	prog.c: In function ‘profile_read_values’:
> >>> 	prog.c:1650:29: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>> 	 1650 |  __u32 m, cpu, num_cpu = obj->rodata->num_cpu;
> >>> 	      |                             ^~
> >>> 	prog.c: In function ‘profile_open_perf_events’:
> >>> 	prog.c:1810:19: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>> 	 1810 |   sizeof(int), obj->rodata->num_cpu * obj->rodata->num_metric);
> >>> 	      |                   ^~
> >>> 	prog.c:1810:42: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>> 	 1810 |   sizeof(int), obj->rodata->num_cpu * obj->rodata->num_metric);
> >>> 	      |                                          ^~
> >>> 	prog.c:1825:26: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>> 	 1825 |   for (cpu = 0; cpu < obj->rodata->num_cpu; cpu++) {
> >>> 	      |                          ^~
> >>> 	prog.c: In function ‘do_profile’:
> >>> 	prog.c:1904:13: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>> 	 1904 |  profile_obj->rodata->num_cpu = num_cpu;
> >>> 	      |             ^~
> >>> 	prog.c:1905:13: error: ‘struct profiler_bpf’ has no member named ‘rodata’
> >>> 	 1905 |  profile_obj->rodata->num_metric = num_metric;
> >>> 	      |             ^~
> >>> 	make: *** [Makefile:129: prog.o] Error 1
> >> 
> >> I guess you need a newer version of clang that supports global data in BPF programs. 
> >> 
> >> Thanks,
> >> Song
> >> 
> > 
> > Thinking about this requirement again... Do you think it would be worth
> > adding (as a follow-up) a feature check on the availability of clang
> > with global data support to bpftool's Makefile? So that we could compile
> > out program profiling if clang is not present or does not support it.
> > Just like libbfd support is optional already.
> > 
> > I'm asking mostly because a number of distributions now package bpftool,
> > and e.g. Ubuntu builds it from kernel source when creating its
> > linux-images and linux-tools-* packages. And I am pretty sure the build
> > environment does not have latest clang/LLVM, but it would be great to
> > remain able to build bpftool.
> 
> Yeah, I think it is a good idea. Some more Makefile fun. ;)

I think it's good idea, also bpftool is already using feature
detection from tools/build/features.. you can check commits like:

  fb982666e380 tools/bpftool: fix bpftool build with bintutils >= 2.9

for adding new feature detection

jirka