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

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Message-ID: <CAL+tcoA8Yhk85mkOBE9jEx7fd1s5rAW+Y8Uf2DAaNR3-9DW0Vg@mail.gmail.com>
Date: Thu, 3 Jul 2025 07:09:09 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, bjorn@...nel.org, magnus.karlsson@...el.com, 
	maciej.fijalkowski@...el.com, jonathan.lemon@...il.com, sdf@...ichev.me, 
	ast@...nel.org, daniel@...earbox.net, hawk@...nel.org, 
	john.fastabend@...il.com, joe@...a.to, willemdebruijn.kernel@...il.com, 
	bpf@...r.kernel.org, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v5 2/2] selftests/bpf: add a new test to check
 the consumer update case

On Thu, Jul 3, 2025 at 12:03 AM Stanislav Fomichev <stfomichev@...il.com> wrote:
>
> On 07/02, Jason Xing wrote:
> > From: Jason Xing <kernelxing@...cent.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@...cent.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?

Thanks,
Jason