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@xxxxxxxxx>
> > > > ---
> > > > 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.
