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SubjectRe: [PATCH] bpf: added the account of BPF running time
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On 9/2/22 12:12 PM, Yunhui Cui wrote:
[...]
> index a5f21dc3c432..9cb072f9e32b 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -565,6 +565,12 @@ struct sk_filter {
> struct bpf_prog *prog;
> };
>
> +struct bpf_account {
> + u64_stats_t nsecs;
> + struct u64_stats_sync syncp;
> +};
> +DECLARE_PER_CPU(struct bpf_account, bpftime);
> +
> DECLARE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
>
> typedef unsigned int (*bpf_dispatcher_fn)(const void *ctx,
> @@ -577,12 +583,14 @@ static __always_inline u32 __bpf_prog_run(const struct bpf_prog *prog,
> bpf_dispatcher_fn dfunc)
> {
> u32 ret;
> + struct bpf_account *bact;
> + unsigned long flags;
> + u64 start = 0;
>
> cant_migrate();
> + start = sched_clock();
> if (static_branch_unlikely(&bpf_stats_enabled_key)) {
> struct bpf_prog_stats *stats;
> - u64 start = sched_clock();
> - unsigned long flags;
>
> ret = dfunc(ctx, prog->insnsi, prog->bpf_func);
> stats = this_cpu_ptr(prog->stats);
> @@ -593,6 +601,11 @@ static __always_inline u32 __bpf_prog_run(const struct bpf_prog *prog,
> } else {
> ret = dfunc(ctx, prog->insnsi, prog->bpf_func);
> }
> + bact = this_cpu_ptr(&bpftime);
> + flags = u64_stats_update_begin_irqsave(&bact->syncp);
> + u64_stats_add(&bact->nsecs, sched_clock() - start);
> + u64_stats_update_end_irqrestore(&bact->syncp, flags);
> +
> return ret;

The overhead this adds unconditionally is no-go. Have you tried using/improving:

commit 47c09d6a9f6794caface4ad50930460b82d7c670
Author: Song Liu <songliubraving@fb.com>
Date: Mon Mar 9 10:32:15 2020 -0700

bpftool: Introduce "prog profile" command

With fentry/fexit programs, it is possible to profile BPF program with
hardware counters. Introduce bpftool "prog profile", which measures key
metrics of a BPF program.

bpftool prog profile command creates per-cpu perf events. Then it attaches
fentry/fexit programs to the target BPF program. The fentry program saves
perf event value to a map. The fexit program reads the perf event again,
and calculates the difference, which is the instructions/cycles used by
the target program.

Example input and output:

./bpftool prog profile id 337 duration 3 cycles instructions llc_misses

4228 run_cnt
3403698 cycles (84.08%)
3525294 instructions # 1.04 insn per cycle (84.05%)
13 llc_misses # 3.69 LLC misses per million isns (83.50%)

This command measures cycles and instructions for BPF program with id
337 for 3 seconds. The program has triggered 4228 times. The rest of the
output is similar to perf-stat. [...]

Thanks,
Daniel

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