| Age | Commit message (Collapse) | Author |
|---|
|
Utilize bpf_modify_return_test_tp() kfunc to have a fast way to trigger
tp/raw_tp/fmodret programs from another BPF program, which gives us
comparable batched benchmarks to (batched) kprobe/fentry benchmarks.
We don't switch kprobe/fentry batched benchmarks to this kfunc to make
bench tool usable on older kernels as well.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240326162151.3981687-7-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
|
|
Remove "legacy" benchmarks triggered by syscalls in favor of newly added
in-kernel/batched benchmarks. Drop -batched suffix now as well.
Next patch will restore "feature parity" by adding back
tp/raw_tp/fmodret benchmarks based on in-kernel kfunc approach.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240326162151.3981687-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
|
|
Existing kprobe/fentry triggering benchmarks have 1-to-1 mapping between
one syscall execution and BPF program run. While we use a fast
get_pgid() syscall, syscall overhead can still be non-trivial.
This patch adds kprobe/fentry set of benchmarks significantly amortizing
the cost of syscall vs actual BPF triggering overhead. We do this by
employing BPF_PROG_TEST_RUN command to trigger "driver" raw_tp program
which does a tight parameterized loop calling cheap BPF helper
(bpf_get_numa_node_id()), to which kprobe/fentry programs are
attached for benchmarking.
This way 1 bpf() syscall causes N executions of BPF program being
benchmarked. N defaults to 100, but can be adjusted with
--trig-batch-iters CLI argument.
For comparison we also implement a new baseline program that instead of
triggering another BPF program just does N atomic per-CPU counter
increments, establishing the limit for all other types of program within
this batched benchmarking setup.
Taking the final set of benchmarks added in this patch set (including
tp/raw_tp/fmodret, added in later patch), and keeping for now "legacy"
syscall-driven benchmarks, we can capture all triggering benchmarks in
one place for comparison, before we remove the legacy ones (and rename
xxx-batched into just xxx).
$ benchs/run_bench_trigger.sh
usermode-count : 79.500 ± 0.024M/s
kernel-count : 49.949 ± 0.081M/s
syscall-count : 9.009 ± 0.007M/s
fentry-batch : 31.002 ± 0.015M/s
fexit-batch : 20.372 ± 0.028M/s
fmodret-batch : 21.651 ± 0.659M/s
rawtp-batch : 36.775 ± 0.264M/s
tp-batch : 19.411 ± 0.248M/s
kprobe-batch : 12.949 ± 0.220M/s
kprobe-multi-batch : 15.400 ± 0.007M/s
kretprobe-batch : 5.559 ± 0.011M/s
kretprobe-multi-batch: 5.861 ± 0.003M/s
fentry-legacy : 8.329 ± 0.004M/s
fexit-legacy : 6.239 ± 0.003M/s
fmodret-legacy : 6.595 ± 0.001M/s
rawtp-legacy : 8.305 ± 0.004M/s
tp-legacy : 6.382 ± 0.001M/s
kprobe-legacy : 5.528 ± 0.003M/s
kprobe-multi-legacy : 5.864 ± 0.022M/s
kretprobe-legacy : 3.081 ± 0.001M/s
kretprobe-multi-legacy: 3.193 ± 0.001M/s
Note how xxx-batch variants are measured with significantly higher
throughput, even though it's exactly the same in-kernel overhead. As
such, results can be compared only between benchmarks of the same kind
(syscall vs batched):
fentry-legacy : 8.329 ± 0.004M/s
fentry-batch : 31.002 ± 0.015M/s
kprobe-multi-legacy : 5.864 ± 0.022M/s
kprobe-multi-batch : 15.400 ± 0.007M/s
Note also that syscall-count is setting a theoretical limit for
syscall-triggered benchmarks, while kernel-count is setting similar
limits for batch variants. usermode-count is a happy and unachievable
case of user space counting without doing any syscalls, and is mostly
the measure of CPU speed for such a trivial benchmark.
As was mentioned, tp/raw_tp/fmodret require kernel-side kfunc to produce
similar benchmark, which we address in a separate patch.
Note that run_bench_trigger.sh allows to override a list of benchmarks
to run, which is very useful for performance work.
Cc: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240326162151.3981687-3-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
|
|
It is sometimes desirable to be able to trigger BPF program from user-space
with minimal overhead. sys_enter would seem to be a good candidate, yet in
a lot of cases there will be a lot of noise from syscalls triggered by other
processes on the system. So while searching for low-overhead alternative, I've
stumbled upon getpgid() syscall, which seems to be specific enough to not
suffer from accidental syscall by other apps.
This set of benchmarks compares tp, raw_tp w/ filtering by syscall ID, kprobe,
fentry and fmod_ret with returning error (so that syscall would not be
executed), to determine the lowest-overhead way. Here are results on my
machine (using benchs/run_bench_trigger.sh script):
base : 9.200 ± 0.319M/s
tp : 6.690 ± 0.125M/s
rawtp : 8.571 ± 0.214M/s
kprobe : 6.431 ± 0.048M/s
fentry : 8.955 ± 0.241M/s
fmodret : 8.903 ± 0.135M/s
So it seems like fmodret doesn't give much benefit for such lightweight
syscall. Raw tracepoint is pretty decent despite additional filtering logic,
but it will be called for any other syscall in the system, which rules it out.
Fentry, though, seems to be adding the least amoung of overhead and achieves
97.3% of performance of baseline no-BPF-attached syscall.
Using getpgid() seems to be preferable to set_task_comm() approach from
test_overhead, as it's about 2.35x faster in a baseline performance.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200512192445.2351848-5-andriin@fb.com
|
