Re: [PATCH v2 bpf-next 1/2] bpftool: introduce "prog profile" command

On Feb 29, 2020, at 7:52 PM, Yonghong Song [off-list ref] wrote:



On 2/28/20 3:40 PM, Song Liu wrote:

quoted

With fentry/fexit programs, it is possible to profile BPF program with
hardware counters. Introduce bpftool "prog profile", which measures key
metrics of a BPF program.
bpftool prog profile command creates per-cpu perf events. Then it attaches
fentry/fexit programs to the target BPF program. The fentry program saves
perf event value to a map. The fexit program reads the perf event again,
and calculates the difference, which is the instructions/cycles used by
the target program.
Example input and output:
  ./bpftool prog profile 3 id 337 cycles instructions llc_misses
        4228 run_cnt
     3403698 cycles                                              (84.08%)
     3525294 instructions   #  1.04 insn per cycle               (84.05%)
          13 llc_misses     #  3.69 LLC misses per million isns  (83.50%)
This command measures cycles and instructions for BPF program with id
337 for 3 seconds. The program has triggered 4228 times. The rest of the
output is similar to perf-stat. In this example, the counters were only
counting ~84% of the time because of time multiplexing of perf counters.
Note that, this approach measures cycles and instructions in very small
increments. So the fentry/fexit programs introduce noticeable errors to
the measurement results.
The fentry/fexit programs are generated with BPF skeletons. Therefore, we
build bpftool twice. The first time _bpftool is built without skeletons.
Then, _bpftool is used to generate the skeletons. The second time, bpftool
is built with skeletons.
Signed-off-by: Song Liu <redacted>
---
 tools/bpf/bpftool/Makefile                |  18 +
 tools/bpf/bpftool/prog.c                  | 428 +++++++++++++++++++++-
 tools/bpf/bpftool/skeleton/profiler.bpf.c | 171 +++++++++
 tools/bpf/bpftool/skeleton/profiler.h     |  47 +++
 tools/scripts/Makefile.include            |   1 +
 5 files changed, 664 insertions(+), 1 deletion(-)
 create mode 100644 tools/bpf/bpftool/skeleton/profiler.bpf.c
 create mode 100644 tools/bpf/bpftool/skeleton/profiler.h

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index c4e810335810..c035fc107027 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile

@@ -59,6 +59,7 @@ LIBS = $(LIBBPF) -lelf -lz
   INSTALL ?= install
 RM ?= rm -f
+CLANG ?= clang
   FEATURE_USER = .bpftool
 FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib

@@ -110,6 +111,22 @@ SRCS += $(BFD_SRCS)
 endif
   OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
+_OBJS = $(filter-out $(OUTPUT)prog.o,$(OBJS)) $(OUTPUT)_prog.o
+
+$(OUTPUT)_prog.o: prog.c
+	$(QUIET_CC)$(COMPILE.c) -MMD -DBPFTOOL_WITHOUT_SKELETONS -o $@ $<
+
+$(OUTPUT)_bpftool: $(_OBJS) $(LIBBPF)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(_OBJS) $(LIBS)
+
+skeleton/profiler.bpf.o: skeleton/profiler.bpf.c
+	$(QUIET_CLANG)$(CLANG) -g -O2 -target bpf -c $< -o $@

With a fresh checkout, applying this patch and just selftests like
 make -C tools/testing/selftests/bpf

I got the following build error:

make[2]: Leaving directory `/data/users/yhs/work/net-next/tools/lib/bpf'
clang -g -O2 -target bpf -c skeleton/profiler.bpf.c -o skeleton/profiler.bpf.o
skeleton/profiler.bpf.c:5:10: fatal error: 'bpf/bpf_helpers.h' file not found
#include <bpf/bpf_helpers.h>
        ^~~~~~~~~~~~~~~~~~~
1 error generated.
make[1]: *** [skeleton/profiler.bpf.o] Error 1

I think Makefile should be tweaked to avoid selftest failure.

Hmm... I am not seeing this error. The build succeeded in the test. 

Thanks,
Song