linux-kernel - Re: [PATCH bpf-next 5/5] selftests/bpf: add benchmark for uprobe vs. user

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Date:   Mon, 3 Aug 2020 04:47:47 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Xu <dlxu@...com>
Subject: Re: [PATCH bpf-next 5/5] selftests/bpf: add benchmark for uprobe vs.
 user_prog


> On Aug 2, 2020, at 6:51 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> 
> On Sat, Aug 1, 2020 at 1:50 AM Song Liu <songliubraving@...com> wrote:
>> 
>> Add a benchmark to compare performance of
>>  1) uprobe;
>>  2) user program w/o args;
>>  3) user program w/ args;
>>  4) user program w/ args on random cpu.
>> 
> 
> Can you please add it to the existing benchmark runner instead, e.g.,
> along the other bench_trigger benchmarks? No need to re-implement
> benchmark setup. And also that would also allow to compare existing
> ways of cheaply triggering a program vs this new _USER program?

Will try. 

> 
> If the performance is not significantly better than other ways, do you
> think it still makes sense to add a new BPF program type? I think
> triggering KPROBE/TRACEPOINT from bpf_prog_test_run() would be very
> nice, maybe it's possible to add that instead of a new program type?
> Either way, let's see comparison with other program triggering
> mechanisms first.

Triggering KPROBE and TRACEPOINT from bpf_prog_test_run() will be useful. 
But I don't think they can be used instead of user program, for a couple
reasons. First, KPROBE/TRACEPOINT may be triggered by other programs 
running in the system, so user will have to filter those noise out in
each program. Second, it is not easy to specify CPU for KPROBE/TRACEPOINT,
while this feature could be useful in many cases, e.g. get stack trace 
on a given CPU. 

Thanks,
Song