Messages in this thread | | | Date | Wed, 15 Dec 2021 19:55:51 +0000 | Subject | Re: [PATCH v3] cgroup/bpf: fast path skb BPF filtering | From | Pavel Begunkov <> |
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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: >>> On 12/15, Pavel Begunkov wrote: >>>> On 12/15/21 17:33, sdf@google.com wrote: >>>>> On 12/15, Pavel Begunkov wrote: >>>>>> On 12/15/21 16:51, sdf@google.com wrote: >>>>>>> On 12/15, Pavel Begunkov wrote: >>>>>>>> � /* Wrappers for __cgroup_bpf_run_filter_skb() guarded by cgroup_bpf_enabled. */ >>>>>>>> � #define BPF_CGROUP_RUN_PROG_INET_INGRESS(sk, skb)����������������� \ >>>>>>>> � ({����������������������������������������� \ >>>>>>>> ����� int __ret = 0;��������������������������������� \ >>>>>>>> -��� if (cgroup_bpf_enabled(CGROUP_INET_INGRESS))������������� \ >>>>>>>> +��� if (cgroup_bpf_enabled(CGROUP_INET_INGRESS) && sk &&������������� \ >>>>>>>> +������� CGROUP_BPF_TYPE_ENABLED((sk), CGROUP_INET_INGRESS))���������� \ >>>>>>> >>>>>>> Why not add this __cgroup_bpf_run_filter_skb check to >>>>>>> __cgroup_bpf_run_filter_skb? Result of sock_cgroup_ptr() is already there >>>>>>> and you can use it. Maybe move the things around if you want >>>>>>> it to happen earlier. >>>>> >>>>>> For inlining. Just wanted to get it done right, otherwise I'll likely be >>>>>> returning to it back in a few months complaining that I see measurable >>>>>> overhead from the function call :) >>>>> >>>>> Do you expect that direct call to bring any visible overhead? >>>>> Would be nice to compare that inlined case vs >>>>> __cgroup_bpf_prog_array_is_empty inside of __cgroup_bpf_run_filter_skb >>>>> while you're at it (plus move offset initialization down?). >>> >>>> Sorry but that would be waste of time. I naively hope it will be visible >>>> with net at some moment (if not already), that's how it was with io_uring, >>>> that's what I see in the block layer. And in anyway, if just one inlined >>>> won't make a difference, then 10 will. >>> >>> 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.
I'm skeptical I'll be able to measure inlining one function, variability between boots/runs is usually greater and would hide it.
> But tbf I don't understand how it all plays out with the io_uring.
1 syscall per N requests (N=32 IIRC), 1 fdget() per N, no payload page referencing (for zc), and so on
> (mostly trying to understand where there is some gain left on the > table for TCP_ZEROCOPY_RECEIVE).
-- Pavel Begunkov
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