Messages in this thread | | | Subject | Re: [PATCH] bpf: added the account of BPF running time | From | Daniel Borkmann <> | Date | Fri, 2 Sep 2022 17:38:51 +0200 |
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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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