Re: [PATCH v4 bpf-next/net 5/5] selftest: bpf: Add test for SK_BPF_MEMCG_SOCK_ISOLATED.

[Kuniyuki Iwashima <kuniyu@google.com>]

On Wed, Sep 3, 2025 at 9:59 AM Kuniyuki Iwashima <kuniyu@google.com> wrote:
>
> On Tue, Sep 2, 2025 at 1:49 PM Kuniyuki Iwashima <kuniyu@google.com> wrote:
> >
> > On Tue, Sep 2, 2025 at 1:26 PM Martin KaFai Lau <martin.lau@linux.dev> wrote:
> > >
> > > On 8/28/25 6:00 PM, Kuniyuki Iwashima wrote:
> > > > The test does the following for IPv4/IPv6 x TCP/UDP sockets
> > > > with/without BPF prog.
> > > >
> > > >    1. Create socket pairs
> > > >    2. Send a bunch of data that requires more than 256 pages
> > > >    3. Read memory_allocated from the 3rd column in /proc/net/protocols
> > > >    4. Check if unread data is charged to memory_allocated
> > > >
> > > > If BPF prog is attached, memory_allocated should not be changed,
> > > > but we allow a small error (up to 10 pages) in case other processes
> > > > on the host use some amounts of TCP/UDP memory.
> > > >
> > > > At 2., the test actually sends more than 1024 pages because the sysctl
> > > > net.core.mem_pcpu_rsv is 256 is by default, which means 256 pages are
> > > > buffered per cpu before reporting to sk->sk_prot->memory_allocated.
> > > >
> > > >    BUF_SINGLE (1024) * NR_SEND (64) * NR_SOCKETS (64) / 4096
> > > >    = 1024 pages
> > > >
> > > > When I reduced it to 512 pages, the following assertion for the
> > > > non-isolated case got flaky.
> > > >
> > > >    ASSERT_GT(memory_allocated[1], memory_allocated[0] + 256, ...)
> > > >
> > > > Another contributor to slowness is 150ms sleep to make sure 1 RCU
> > > > grace period passes because UDP recv queue is destroyed after that.
> > >
> > > There is a kern_sync_rcu() in testing_helpers.c.
> >
> > Nice helper :)  Will use it.
> >
> > >
> > > >
> > > >    # time ./test_progs -t sk_memcg
> > > >    #370/1   sk_memcg/TCP       :OK
> > > >    #370/2   sk_memcg/UDP       :OK
> > > >    #370/3   sk_memcg/TCPv6     :OK
> > > >    #370/4   sk_memcg/UDPv6     :OK
> > > >    #370     sk_memcg:OK
> > > >    Summary: 1/4 PASSED, 0 SKIPPED, 0 FAILED
> > > >
> > > >    real       0m1.214s
> > > >    user       0m0.014s
> > > >    sys        0m0.318s
> > >
> > > Thanks. It finished much faster in my setup also comparing with the earlier
> > > revision. However, it is a bit flaky when I run it in a loop:
> > >
> > > check_isolated:FAIL:not isolated unexpected not isolated: actual 861 <= expected 861
> > >
> > > I usually can hit this at ~40-th iteration.
> >
> > Oh.. I tested ~10 times manually but will try in a tight loop.
>
> This didn't reproduce on my QEMU with/without --enable-kvm.
>
> Changing the assert from _GT to _GE will address the very case
> above, but I'm not sure if it's enough.

I doubled NR_SEND and it was still faster with kern_sync_rcu()
than usleep(), so I'll simply double NR_SEND in v5

# time ./test_progs -t sk_memcg
...
Summary: 1/4 PASSED, 0 SKIPPED, 0 FAILED
real 0m0.483s
user 0m0.010s
sys 0m0.191s


>
> Does the bpf CI run tests repeatedly or is this only a manual
> scenario ?