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bpf: Add bpf_ktime_get_coarse_ns helper

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The helper uses CLOCK_MONOTONIC_COARSE source of time that is less
accurate but more performant.

We have a BPF CGROUP_SKB firewall that supports event logging through
bpf_perf_event_output(). Each event has a timestamp and currently we use
bpf_ktime_get_ns() for it. Use of bpf_ktime_get_coarse_ns() saves ~15-20
ns in time required for event logging.

bpf_ktime_get_ns():
EgressLogByRemoteEndpoint                              113.82ns    8.79M

bpf_ktime_get_coarse_ns():
EgressLogByRemoteEndpoint                               95.40ns   10.48M

Signed-off-by: Dmitrii Banshchikov <me@ubique.spb.ru>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20201117184549.257280-1-me@ubique.spb.ru
This commit is contained in:
Dmitrii Banshchikov
2020-11-17 18:45:49 +00:00
committed by Daniel Borkmann
parent ea87ae85c9
commit d055126180
6 changed files with 39 additions and 0 deletions
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11
include/uapi/linux/bpf.h
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@@ -3797,6 +3797,16 @@ union bpf_attr {
* is cleared if the flag is not specified.
* Return
* **-EINVAL** if invalid *flags* are passed, zero otherwise.
*
* u64 bpf_ktime_get_coarse_ns(void)
* Description
* Return a coarse-grained version of the time elapsed since
* system boot, in nanoseconds. Does not include time the system
* was suspended.
*
* See: **clock_gettime**\ (**CLOCK_MONOTONIC_COARSE**)
* Return
* Current *ktime*.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3959,6 +3969,7 @@ union bpf_attr {
FN(task_storage_delete), \
FN(get_current_task_btf), \
FN(bprm_opts_set), \
FN(ktime_get_coarse_ns), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper