Messages in this thread | | | Date | Sat, 11 Dec 2021 02:20:13 +0000 | Subject | Re: [BPF PATCH for-next] cgroup/bpf: fast path for not loaded skb BPF filtering | From | Pavel Begunkov <> |
| |
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
-- Pavel Begunkov
| |