Messages in this thread | | | Date | Thu, 16 Dec 2021 13:21:26 +0000 | Subject | Re: [PATCH v3] cgroup/bpf: fast path skb BPF filtering | From | Pavel Begunkov <> |
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On 12/15/21 22:07, Stanislav Fomichev wrote: > On Wed, Dec 15, 2021 at 11:55 AM Pavel Begunkov <asml.silence@gmail.com> wrote: >> >> On 12/15/21 19:15, Stanislav Fomichev wrote: >>> On Wed, Dec 15, 2021 at 10:54 AM Pavel Begunkov <asml.silence@gmail.com> wrote: >>>> >>>> On 12/15/21 18:24, sdf@google.com wrote: [...] >>>>> I can probably do more experiments on my side once your patch is >>>>> accepted. I'm mostly concerned with getsockopt(TCP_ZEROCOPY_RECEIVE). >>>>> If you claim there is visible overhead for a direct call then there >>>>> should be visible benefit to using CGROUP_BPF_TYPE_ENABLED there as >>>>> well. >>>> >>>> Interesting, sounds getsockopt might be performance sensitive to >>>> someone. >>>> >>>> FWIW, I forgot to mention that for testing tx I'm using io_uring >>>> (for both zc and not) with good submission batching. >>> >>> Yeah, last time I saw 2-3% as well, but it was due to kmalloc, see >>> more details in 9cacf81f8161, it was pretty visible under perf. >>> That's why I'm a bit skeptical of your claims of direct calls being >>> somehow visible in these 2-3% (even skb pulls/pushes are not 2-3%?). >> >> migrate_disable/enable together were taking somewhat in-between >> 1% and 1.5% in profiling, don't remember the exact number. The rest >> should be from rcu_read_lock/unlock() in BPF_PROG_RUN_ARRAY_CG_FLAGS() >> and other extra bits on the way. > > You probably have a preemptiple kernel and preemptible rcu which most > likely explains why you see the overhead and I won't (non-preemptible > kernel in our env, rcu_read_lock is essentially a nop, just a compiler > barrier).
Right. For reference tried out non-preemptible, perf shows the function taking 0.8% with a NIC and 1.2% with a dummy netdev.
>> I'm skeptical I'll be able to measure inlining one function, >> variability between boots/runs is usually greater and would hide it. > > Right, that's why I suggested to mirror what we do in set/getsockopt > instead of the new extra CGROUP_BPF_TYPE_ENABLED. But I'll leave it up > to you, Martin and the rest.
-- Pavel Begunkov
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