Re: [PATCH net-next v5 2/2] selftests/bpf: add a new test to check the consumer update case

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Thu, Jul 03, 2025 at 07:09:09AM +0800, Jason Xing wrote:
> On Thu, Jul 3, 2025 at 12:03 AM Stanislav Fomichev <stfomichev@gmail.com> wrote:
> >
> > On 07/02, Jason Xing wrote:
> > > From: Jason Xing <kernelxing@tencent.com>
> > >
> > > The subtest sends 33 packets at one time on purpose to see if xsk
> > > exitting __xsk_generic_xmit() updates the global consumer of tx queue
> > > when reaching the max loop (max_tx_budget, 32 by default). The number 33
> > > can avoid xskq_cons_peek_desc() updates the consumer when it's about to
> > > quit sending, to accurately check if the issue that the first patch
> > > resolves remains. The new case will not check this issue in zero copy
> > > mode.
> > >
> > > Signed-off-by: Jason Xing <kernelxing@tencent.com>
> > > ---
> > > v5
> > > Link: https://lore.kernel.org/all/20250627085745.53173-1-kerneljasonxing@gmail.com/
> > > 1. use the initial approach to add a new testcase
> > > 2. add a new flag 'check_consumer' to see if the check is needed
> > > ---
> > >  tools/testing/selftests/bpf/xskxceiver.c | 51 +++++++++++++++++++++++-
> > >  tools/testing/selftests/bpf/xskxceiver.h |  1 +
> > >  2 files changed, 51 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
> > > index 0ced4026ee44..ed12a55ecf2a 100644
> > > --- a/tools/testing/selftests/bpf/xskxceiver.c
> > > +++ b/tools/testing/selftests/bpf/xskxceiver.c
> > > @@ -109,6 +109,8 @@
> > >
> > >  #include <network_helpers.h>
> > >
> > > +#define MAX_TX_BUDGET_DEFAULT 32
> > > +
> > >  static bool opt_verbose;
> > >  static bool opt_print_tests;
> > >  static enum test_mode opt_mode = TEST_MODE_ALL;
> > > @@ -1091,11 +1093,45 @@ static bool is_pkt_valid(struct pkt *pkt, void *buffer, u64 addr, u32 len)
> > >       return true;
> > >  }
> > >
> > > +static u32 load_value(u32 *counter)
> > > +{
> > > +     return __atomic_load_n(counter, __ATOMIC_ACQUIRE);
> > > +}
> > > +
> > > +static bool kick_tx_with_check(struct xsk_socket_info *xsk, int *ret)
> > > +{
> > > +     u32 max_budget = MAX_TX_BUDGET_DEFAULT;
> > > +     u32 cons, ready_to_send;
> > > +     int delta;
> > > +
> > > +     cons = load_value(xsk->tx.consumer);
> > > +     ready_to_send = load_value(xsk->tx.producer) - cons;
> > > +     *ret = sendto(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, 0);
> > > +
> > > +     delta = load_value(xsk->tx.consumer) - cons;
> > > +     /* By default, xsk should consume exact @max_budget descs at one
> > > +      * send in this case where hitting the max budget limit in while
> > > +      * loop is triggered in __xsk_generic_xmit(). Please make sure that
> > > +      * the number of descs to be sent is larger than @max_budget, or
> > > +      * else the tx.consumer will be updated in xskq_cons_peek_desc()
> > > +      * in time which hides the issue we try to verify.
> > > +      */
> > > +     if (ready_to_send > max_budget && delta != max_budget)
> > > +             return false;
> > > +
> > > +     return true;
> > > +}
> > > +
> > >  static int kick_tx(struct xsk_socket_info *xsk)
> > >  {
> > >       int ret;
> > >
> > > -     ret = sendto(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, 0);
> > > +     if (xsk->check_consumer) {
> > > +             if (!kick_tx_with_check(xsk, &ret))
> > > +                     return TEST_FAILURE;
> > > +     } else {
> > > +             ret = sendto(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, 0);
> > > +     }
> > >       if (ret >= 0)
> > >               return TEST_PASS;
> > >       if (errno == ENOBUFS || errno == EAGAIN || errno == EBUSY || errno == ENETDOWN) {
> > > @@ -2613,6 +2649,18 @@ static int testapp_adjust_tail_grow_mb(struct test_spec *test)
> > >                                  XSK_UMEM__LARGE_FRAME_SIZE * 2);
> > >  }
> > >
> > > +static int testapp_tx_queue_consumer(struct test_spec *test)
> > > +{
> > > +     int nr_packets = MAX_TX_BUDGET_DEFAULT + 1;
> > > +
> > > +     pkt_stream_replace(test, nr_packets, MIN_PKT_SIZE);
> > > +     test->ifobj_tx->xsk->batch_size = nr_packets;
> > > +     if (!(test->mode & TEST_MODE_ZC))
> > > +             test->ifobj_tx->xsk->check_consumer = true;
> >
> > The test looks good to me, thank you!
> 
> Thanks.
> 
> >
> > One question here: why not exit/return for TEST_MODE_ZC instead
> > of conditionally setting check_consumer?
> 
> As you said, yes, we could skip the zc test for this
> testapp_tx_queue_consumer(). It doesn't affect the goal or result of
> the subtest. So do you expect me to respin this patch or just leave it
> as is?

Yes I think it would be worth respinning and skipping it for zc. see how
testapp_stats_rx_dropped() does it.

Otherwise we would probably never change it and just keep on running this
test case for zc which is not beneficial at this point.

Besides LGTM!

> 
> Thanks,
> Jason