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. 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 get CLOCK_MONOTONIC_RAW values. The reason to have these functions is to avoid overhead added by a bpf_ktime_get_ns() call in case of benchmarking, when two timestamps are taken to get delta value. With both functions being JITed, the overhead is minimal and the result has better precision. New functions can be used to benchmark BPF code directly in the program, or can be used in kprobe/uprobe to store timestamp counter in the session coockie and then in kretprobe/uretprobe the delta can be calculated and converted into nanoseconds. Pre-requriement for this patch is to adjust CONFIG_BPF_JIT to depend on CONFIG_BPF_SYSCALL as it simplify things and it's actually a long overdue patch. Selftests are also added to check whether the JIT implementation is correct and to show the simplest usage example. Change log: v11 -> v12: * drop x86_32 JIT implementation because previous implementation of mul_u64_u32_shr() was not fully correct and the amount of work to properly implement it in asm is not worth the result. * add comment explaining stablility of shift and mult values * add comment explaining the reasoning behind CLOCK_MONOTONIC_RAW usage in fallback mode * drop KF_FASTCALL tag from bpf_get_cpu_time_counter() as it cannot be implemented as fastcall in the verifier * re-implement verifier checks for possible JIT of kfuncs * adjust selftests to use JIT code for x86_64 and verifier inlining for arm64 v10 -> v11: * add missing IS_ENABLED(CONFIG_BPF_SYSCALL) * reword "cycles" -> "counter" v9 -> v10: * rework fallback implementation to avoid using vDSO data from kernel space. * add comment about using "LFENCE; RDTSC" instead of "RDTSCP" * guard x86 JIT implementation to be sure that TSC is enabled and stable * v9 link: https://lore.kernel.org/bpf/20241123005833.810044-1-vadfed@xxxxxxxx/ v8 -> v9: * rewording of commit messages, no code changes * move change log from each patch into cover letter 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 (5): bpf: adjust BPF JIT dependency to BPF_SYSCALL bpf: add bpf_get_cpu_time_counter kfunc bpf: add bpf_cpu_time_counter_to_ns helper selftests/bpf: add selftest to check bpf_get_cpu_time_counter jit selftests/bpf: add usage example for cpu time counter kfuncs arch/x86/net/bpf_jit_comp.c | 70 ++++++++++ arch/x86/net/bpf_jit_comp32.c | 2 + include/linux/bpf.h | 4 + include/linux/filter.h | 1 + kernel/bpf/Kconfig | 2 +- kernel/bpf/core.c | 11 ++ kernel/bpf/helpers.c | 17 +++ kernel/bpf/verifier.c | 13 +- .../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 | 120 ++++++++++++++++++ 12 files changed, 299 insertions(+), 3 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 -- 2.47.1
