[bpf-next,v8,0/4] bpf: add cpu cycles kfuncss

Message

Vadim Fedorenko Nov. 21, 2024, 12:08 a.m. UTC

This patchset adds 2 kfuncs to provide a way to precisely measure the
time spent running some code. The first patch provides a way to get cpu
cycles counter which is used to feed CLOCK_MONOTONIC_RAW. On x86
architecture it is effectively rdtsc_ordered() function while on other
architectures it falls back to __arch_get_hw_counter(). The second patch
adds a kfunc to convert cpu cycles to nanoseconds using shift/mult
constants discovered by kernel. The main use-case for this kfunc is to
convert deltas of timestamp counter values into nanoseconds. It is not
supposed to get CLOCK_MONOTONIC_RAW values as offset part is skipped.
JIT version is done for x86 for now, on other architectures it falls
back to slightly simplified version of vdso_calc_ns.

Selftests are also added to check whether the JIT implementation is
correct and to show the simplest usage example.

Change log:
v7 -> v8:
* rename kfuncs again to bpf_get_cpu_time_counter() and
  bpf_cpu_time_counter_to_ns()
* use cyc2ns_read_begin()/cyc2ns_read_end() to get mult and shift
  constants in bpf_cpu_time_counter_to_ns()
v6 -> v7:
* change boot_cpu_has() to cpu_feature_enabled() (Borislav)
* return constant clock_mode in __arch_get_hw_counter() call
v5 -> v6:
* added cover letter
* add comment about dropping S64_MAX manipulation in jitted
  implementation of rdtsc_oredered (Alexey)
* add comment about using 'lfence;rdtsc' variant (Alexey)
* change the check in fixup_kfunc_call() (Eduard)
* make __arch_get_hw_counter() call more aligned with vDSO
  implementation (Yonghong)
v4 -> v5:
* use #if instead of #ifdef with IS_ENABLED
v3 -> v4:
* change name of the helper to bpf_get_cpu_cycles (Andrii)
* Hide the helper behind CONFIG_GENERIC_GETTIMEOFDAY to avoid exposing
  it on architectures which do not have vDSO functions and data
* reduce the scope of check of inlined functions in verifier to only 2,
  which are actually inlined.
* change helper name to bpf_cpu_cycles_to_ns.
* hide it behind CONFIG_GENERIC_GETTIMEOFDAY to avoid exposing on
  unsupported architectures.
v2 -> v3:
* change name of the helper to bpf_get_cpu_cycles_counter to
  explicitly mention what counter it provides (Andrii)
* move kfunc definition to bpf.h to use it in JIT.
* introduce another kfunc to convert cycles into nanoseconds as
  more meaningful time units for generic tracing use case (Andrii)
v1 -> v2:
* Fix incorrect function return value type to u64
* Introduce bpf_jit_inlines_kfunc_call() and use it in
	mark_fastcall_pattern_for_call() to avoid clobbering in case
	of running programs with no JIT (Eduard)
* Avoid rewriting instruction and check function pointer directly
	in JIT (Alexei)
* Change includes to fix compile issues on non x86 architectures


Vadim Fedorenko (4):
  bpf: add bpf_get_cpu_time_counter kfunc
  bpf: add bpf_cpu_time_counter_to_ns helper
  selftests/bpf: add selftest to check rdtsc jit
  selftests/bpf: add usage example for cpu cycles kfuncs

 arch/x86/net/bpf_jit_comp.c                   |  66 +++++++++++
 arch/x86/net/bpf_jit_comp32.c                 |  41 +++++++
 include/linux/bpf.h                           |   6 +
 include/linux/filter.h                        |   1 +
 kernel/bpf/core.c                             |  11 ++
 kernel/bpf/helpers.c                          |  39 +++++++
 kernel/bpf/verifier.c                         |  41 ++++++-
 .../bpf/prog_tests/test_cpu_cycles.c          |  35 ++++++
 .../selftests/bpf/prog_tests/verifier.c       |   2 +
 .../selftests/bpf/progs/test_cpu_cycles.c     |  25 +++++
 .../selftests/bpf/progs/verifier_cpu_cycles.c | 104 ++++++++++++++++++
 11 files changed, 365 insertions(+), 6 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_cpu_cycles.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_cpu_cycles.c
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_cpu_cycles.c