On 3/1/20 2:37 PM, Song Liu wrote:
On Feb 29, 2020, at 7:52 PM, Yonghong Song <yhs@xxxxxx> wrote:
On 2/28/20 3:40 PM, Song Liu wrote:
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 <songliubraving@xxxxxx>
---
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 $@
With a fresh checkout, applying this patch and just selftests like
make -C tools/testing/selftests/bpf
I got the following build error:
make[2]: Leaving directory `/data/users/yhs/work/net-next/tools/lib/bpf'
clang -g -O2 -target bpf -c skeleton/profiler.bpf.c -o skeleton/profiler.bpf.o
skeleton/profiler.bpf.c:5:10: fatal error: 'bpf/bpf_helpers.h' file not found
#include <bpf/bpf_helpers.h>
^~~~~~~~~~~~~~~~~~~
1 error generated.
make[1]: *** [skeleton/profiler.bpf.o] Error 1
I think Makefile should be tweaked to avoid selftest failure.
Hmm... I am not seeing this error. The build succeeded in the test.
Just tried again with a *fresh* checkout of tools/ directory with the patch.
-bash-4.4$ make -C tools/testing/selftests/bpf
...
LINK
/data/users/yhs/work/net-next/tools/testing/selftests/bpf/tools/build/bpftool//libbpf/libbpf.a
LINK
/data/users/yhs/work/net-next/tools/testing/selftests/bpf/tools/build/bpftool/_bpftool
make[1]: *** No rule to make target `skeleton/profiler.bpf.c', needed by
`skeleton/profiler.bpf.o'. Stop.
make: ***
[/data/users/yhs/work/net-next/tools/testing/selftests/bpf/tools/sbin/bpftool]
Error 2
make: Leaving directory
`/data/users/yhs/work/net-next/tools/testing/selftests/bpf
The error is different from my previous try, but the build still fails.
Thanks,
Song
