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Thu, 21 May 2026 06:53:16 -0700 (PDT) From: Jason Xing To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, willemb@google.com, kuniyu@google.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, memxor@gmail.com, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, Jason Xing Subject: [PATCH net-next v2 1/6] bpf: Add bpf_ktime_get_real_ns() kfunc Date: Thu, 21 May 2026 21:52:39 +0800 Message-Id: <20260521135244.40869-2-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20260521135244.40869-1-kerneljasonxing@gmail.com> References: <20260521135244.40869-1-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jason Xing Currently BPF programs can obtain timestamps via bpf_ktime_get_ns(), which returns CLOCK_MONOTONIC time. However, the skb->tstamp field populated by the network stack uses ktime_get_real() which is in the CLOCK_REALTIME domain. In the series, kernel reports the software/hardware timestamps through sockopt and then userspace bpf application gets them and calculate the delta only through an unified time unit. However, prior to this, when a BPF program tries to measure RX packet delay by comparing skb->tstamp with bpf_ktime_get_ns(), the result is incorrect because the two clocks have different epochs. Introduce a new BPF kfunc bpf_ktime_get_real_ns() that returns the current CLOCK_REALTIME time. This allows BPF programs to perform accurate delay calculations without clock domain mismatch issue. Signed-off-by: Jason Xing --- kernel/bpf/helpers.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 2bb60200c266..863645d096ef 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2317,6 +2317,11 @@ void bpf_rb_root_free(const struct btf_field *field, void *rb_root, __bpf_kfunc_start_defs(); +__bpf_kfunc u64 bpf_ktime_get_real_ns(void) +{ + return ktime_get_real_fast_ns(); +} + /** * bpf_obj_new() - allocate an object described by program BTF * @local_type_id__k: type ID in program BTF @@ -4859,6 +4864,7 @@ BTF_ID_FLAGS(func, bpf_task_work_schedule_resume, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, bpf_dynptr_from_file) BTF_ID_FLAGS(func, bpf_dynptr_file_discard) BTF_ID_FLAGS(func, bpf_timer_cancel_async) +BTF_ID_FLAGS(func, bpf_ktime_get_real_ns) BTF_KFUNCS_END(common_btf_ids) static const struct btf_kfunc_id_set common_kfunc_set = { -- 2.43.7