Messages in this thread | | | Date | Sat, 11 Dec 2021 01:15:05 +0000 | Subject | Re: [BPF PATCH for-next] cgroup/bpf: fast path for not loaded skb BPF filtering | From | Pavel Begunkov <> |
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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.
-- Pavel Begunkov
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