From: sdf@google.com
To: Pavel Begunkov <asml.silence@gmail.com>
Cc: Martin KaFai Lau <kafai@fb.com>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Song Liu <songliubraving@fb.com>,
linux-kernel@vger.kernel.org
Subject: Re: [BPF PATCH for-next] cgroup/bpf: fast path for not loaded skb BPF filtering
Date: Tue, 14 Dec 2021 09:54:16 -0800 [thread overview]
Message-ID: <YbjaSNBlW03rX6c7@google.com> (raw)
In-Reply-To: <fa707ef9-d612-a3a4-1b2a-fc2b28a3ec5f@gmail.com>
On 12/11, Pavel Begunkov wrote:
> On 12/11/21 01:56, Martin KaFai Lau wrote:
> > On Sat, Dec 11, 2021 at 01:15:05AM +0000, Pavel Begunkov wrote:
> > > On 12/11/21 00:38, Martin KaFai Lau wrote:
> > > > On Fri, Dec 10, 2021 at 02:23:34AM +0000, Pavel Begunkov wrote:
> > > > > cgroup_bpf_enabled_key static key guards from overhead in cases
> where
> > > > > no cgroup bpf program of a specific type is loaded in any cgroup.
> Turn
> > > > > out that's not always good enough, e.g. when there are many
> cgroups but
> > > > > ones that we're interesting in are without bpf. It's seen in
> server
> > > > > environments, but the problem seems to be even wider as apparently
> > > > > systemd loads some BPF affecting my laptop.
> > > > >
> > > > > Profiles for small packet or zerocopy transmissions over fast
> network
> > > > > show __cgroup_bpf_run_filter_skb() taking 2-3%, 1% of which is
> from
> > > > > migrate_disable/enable(), and similarly on the receiving side.
> Also
> > > > > got +4-5% of t-put for local testing.
> > > > >
> > > > > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> > > > > ---
> > > > > include/linux/bpf-cgroup.h | 24 +++++++++++++++++++++---
> > > > > kernel/bpf/cgroup.c | 23 +++++++----------------
> > > > > 2 files changed, 28 insertions(+), 19 deletions(-)
> > > > >
> > > > > diff --git a/include/linux/bpf-cgroup.h
> b/include/linux/bpf-cgroup.h
> > > > > index 11820a430d6c..99b01201d7db 100644
> > > > > --- a/include/linux/bpf-cgroup.h
> > > > > +++ b/include/linux/bpf-cgroup.h
> > > > > @@ -141,6 +141,9 @@ struct cgroup_bpf {
> > > > > struct list_head progs[MAX_CGROUP_BPF_ATTACH_TYPE];
> > > > > u32 flags[MAX_CGROUP_BPF_ATTACH_TYPE];
> > > > > + /* for each type tracks whether effective prog array is not
> empty */
> > > > > + unsigned long enabled_mask;
> > > > > +
> > > > > /* list of cgroup shared storages */
> > > > > struct list_head storages;
> > > > > @@ -219,11 +222,25 @@ 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_type_enabled(struct cgroup_bpf
> *cgrp_bpf,
> > > > > + enum cgroup_bpf_attach_type atype)
> > > > > +{
> > > > > + return test_bit(atype, &cgrp_bpf->enabled_mask);
> > > > > +}
> > > > > +
> > > > > +#define CGROUP_BPF_TYPE_ENABLED(sk, atype) \
> > > > > +({ \
> > > > > + struct cgroup *__cgrp =
> sock_cgroup_ptr(&(sk)->sk_cgrp_data); \
> > > > > + \
> > > > > + __cgroup_bpf_type_enabled(&__cgrp->bpf, (atype)); \
> > > > > +})
> > > > I think it should directly test if the array is empty or not
> instead of
> > > > adding another bit.
> > > >
> > > > Can the existing __cgroup_bpf_prog_array_is_empty(cgrp, ...) test
> be used instead?
> > >
> > > That was the first idea, but it's still heavier than I'd wish.
> 0.3%-0.7%
> > > in profiles, something similar in reqs/s. rcu_read_lock/unlock() pair
> is
> > > cheap but anyway adds 2 barrier()s, and with bitmasks we can inline
> > > the check.
> > It sounds like there is opportunity to optimize
> > __cgroup_bpf_prog_array_is_empty().
> >
> > How about using rcu_access_pointer(), testing with
> &empty_prog_array.hdr,
> > and then inline it? The cgroup prog array cannot be all
> > dummy_bpf_prog.prog. If that could be the case, it should be replaced
> > with &empty_prog_array.hdr earlier, so please check.
> I'd need to expose and export empty_prog_array, but that should do.
> Will try it out, thanks
Note that we already use __cgroup_bpf_prog_array_is_empty in
__cgroup_bpf_run_filter_setsockopt/__cgroup_bpf_run_filter_getsockopt
for exactly the same purpose. If you happen to optimize it, pls
update these places as well.
next prev parent reply other threads:[~2021-12-14 17:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-10 2:23 [BPF PATCH for-next] cgroup/bpf: fast path for not loaded skb BPF filtering Pavel Begunkov
2021-12-11 0:38 ` Martin KaFai Lau
2021-12-11 1:15 ` Pavel Begunkov
2021-12-11 1:56 ` Martin KaFai Lau
2021-12-11 2:20 ` Pavel Begunkov
2021-12-14 17:54 ` sdf [this message]
2021-12-14 18:00 ` Pavel Begunkov
2021-12-14 18:04 ` Stanislav Fomichev
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