From: Jason Xing <kerneljasonxing@gmail•com>
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 <kernelxing@tencent•com>
Subject: [PATCH net-next v2 1/6] bpf: Add bpf_ktime_get_real_ns() kfunc
Date: Thu, 21 May 2026 21:52:39 +0800 [thread overview]
Message-ID: <20260521135244.40869-2-kerneljasonxing@gmail.com> (raw)
In-Reply-To: <20260521135244.40869-1-kerneljasonxing@gmail.com>
From: Jason Xing <kernelxing@tencent•com>
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 <kernelxing@tencent•com>
---
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
next prev parent reply other threads:[~2026-05-21 13:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-21 13:52 [PATCH net-next v2 0/6] bpf-timestamp: support rx side Jason Xing
2026-05-21 13:52 ` Jason Xing [this message]
2026-05-21 13:52 ` [PATCH net-next v2 2/6] net: export sock_disable_timestamp() declaration Jason Xing
2026-05-21 13:52 ` [PATCH net-next v2 3/6] bpf: support bpf_setsockopt for bpf timestamping rx feature Jason Xing
2026-05-23 4:02 ` Kuniyuki Iwashima
2026-05-21 13:52 ` [PATCH net-next v2 4/6] bpf: add BPF_SOCK_OPS_TSTAMP_RCV_CB callback Jason Xing
2026-05-21 13:52 ` [PATCH net-next v2 5/6] bpf: enable bpf timestamping rx in TCP layer Jason Xing
2026-05-23 3:45 ` Kuniyuki Iwashima
2026-05-28 0:50 ` Jason Xing
2026-05-21 13:52 ` [PATCH net-next v2 6/6] selftests/bpf: Add RX latency tests for bpf timestamping Jason Xing
2026-05-23 3:47 ` [PATCH net-next v2 0/6] bpf-timestamp: support rx side Kuniyuki Iwashima
2026-05-28 0:50 ` Jason Xing
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