Re: [PATCH v3] cgroup/bpf: fast path skb BPF filtering

[Pavel Begunkov]

On 12/15/21 16:51, sdf@xxxxxxxxxx wrote:
> On 12/15, Pavel Begunkov wrote:
> > Add per socket fast path for not enabled BPF skb filtering, which sheds
> > a nice chunk of send/recv overhead when affected. Testing udp with 128
> > byte payload and/or zerocopy with any payload size showed 2-3%
> > improvement in requests/s on the tx side using fast NICs across network,
> > and around 4% for dummy device. Same goes for rx, not measured, but
> > numbers should be relatable.
> > In my understanding, this should affect a good share of machines, and at
> > least it includes my laptops and some checked servers.
>
> > The core of the problem is that even though there is
> > cgroup_bpf_enabled_key guarding from __cgroup_bpf_run_filter_skb()
> > overhead, there are cases where we have several cgroups and loading a
> > BPF program to one also makes all others to go through the slow path
> > even when they don't have any BPF attached. It's even worse, because
> > apparently systemd or some other early init loads some BPF and so
> > triggers exactly this situation for normal networking.
>
> > Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
> > ---
>
> > v2: replace bitmask appoach with empty_prog_array (suggested by Martin)
> > v3: add "bpf_" prefix to empty_prog_array (Martin)
>
> >   include/linux/bpf-cgroup.h | 24 +++++++++++++++++++++---
> >   include/linux/bpf.h        | 13 +++++++++++++
> >   kernel/bpf/cgroup.c        | 18 ++----------------
> >   kernel/bpf/core.c          | 16 ++++------------
> >   4 files changed, 40 insertions(+), 31 deletions(-)
>
> > diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
> > index 11820a430d6c..c6dacdbdf565 100644
> > --- a/include/linux/bpf-cgroup.h
> > +++ b/include/linux/bpf-cgroup.h
> > @@ -219,11 +219,28 @@ int bpf_percpu_cgroup_storage_copy(struct bpf_map *map, void *key, void *value);
> >   int bpf_percpu_cgroup_storage_update(struct bpf_map *map, void *key,
> >                        void *value, u64 flags);
>
> > +static inline bool
> > +__cgroup_bpf_prog_array_is_empty(struct cgroup_bpf *cgrp_bpf,
> > +                 enum cgroup_bpf_attach_type type)
> > +{
> > +    struct bpf_prog_array *array = rcu_access_pointer(cgrp_bpf->effective[type]);
> > +
> > +    return array == &bpf_empty_prog_array.hdr;
> > +}
> > +
> > +#define CGROUP_BPF_TYPE_ENABLED(sk, atype)                       \
> > +({                                           \
> > +    struct cgroup *__cgrp = sock_cgroup_ptr(&(sk)->sk_cgrp_data);           \
> > +                                           \
> > +    !__cgroup_bpf_prog_array_is_empty(&__cgrp->bpf, (atype));           \
> > +})
> > +
> >   /* 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 :)

--
Pavel Begunkov