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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Stanislav Fomichev <sdf@google.com>
Cc: Jesper Dangaard Brouer <jbrouer@redhat.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	bpf <bpf@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Martin KaFai Lau <martin.lau@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Alexander Lobakin <alexandr.lobakin@intel.com>,
	Larysa Zaremba <larysa.zaremba@intel.com>,
	xdp-hints@xdp-project.net, anthony.l.nguyen@intel.com, "Song,
	Yoong Siang" <yoong.siang.song@intel.com>,
	"Ong, Boon Leong" <boon.leong.ong@intel.com>,
	intel-wired-lan <intel-wired-lan@lists.osuosl.org>,
	Paolo Abeni <pabeni@redhat.com>,
	Jesse Brandeburg <jesse.brandeburg@intel.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	"David S. Miller" <davem@davemloft.net>
Subject: [xdp-hints] Re: [PATCH bpf-next V2 3/6] selftests/bpf: xdp_hw_metadata RX hash return code info
Date: Wed, 22 Mar 2023 12:17:05 -0700	[thread overview]
Message-ID: <CAADnVQ+6FeQ97DZLco3OtbtXQvGUAY4nr5tM++6NEDr+u8m7GQ@mail.gmail.com> (raw)
In-Reply-To: <CAKH8qBuHaaqnV-_mb1Roao9ZDrEHm+1Cj77hPZSRgwxoqphvxQ@mail.gmail.com>

On Wed, Mar 22, 2023 at 12:00 PM Stanislav Fomichev <sdf@google.com> wrote:
>
> On Wed, Mar 22, 2023 at 9:07 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Mar 22, 2023 at 9:05 AM Jesper Dangaard Brouer
> > <jbrouer@redhat.com> wrote:
> > >
> > >
> > >
> > > On 21/03/2023 19.47, Stanislav Fomichev wrote:
> > > > On Tue, Mar 21, 2023 at 6:47 AM Jesper Dangaard Brouer
> > > > <brouer@redhat.com> wrote:
> > > >>
> > > >> When driver developers add XDP-hints kfuncs for RX hash it is
> > > >> practical to print the return code in bpf_printk trace pipe log.
> > > >>
> > > >> Print hash value as a hex value, both AF_XDP userspace and bpf_prog,
> > > >> as this makes it easier to spot poor quality hashes.
> > > >>
> > > >> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> > > >> ---
> > > >>   .../testing/selftests/bpf/progs/xdp_hw_metadata.c  |    9 ++++++---
> > > >>   tools/testing/selftests/bpf/xdp_hw_metadata.c      |    5 ++++-
> > > >>   2 files changed, 10 insertions(+), 4 deletions(-)
> > > >>
> > > >> diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> > > >> index 40c17adbf483..ce07010e4d48 100644
> > > >> --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> > > >> +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> > > >> @@ -77,10 +77,13 @@ int rx(struct xdp_md *ctx)
> > > >>                  meta->rx_timestamp = 0; /* Used by AF_XDP as not avail signal */
> > > >>          }
> > > >>
> > > >> -       if (!bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash))
> > > >> -               bpf_printk("populated rx_hash with %u", meta->rx_hash);
> > > >> -       else
> > > >> +       ret = bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash);
> > > >> +       if (ret >= 0) {
> > > >> +               bpf_printk("populated rx_hash with 0x%08X", meta->rx_hash);
> > > >> +       } else {
> > > >> +               bpf_printk("rx_hash not-avail errno:%d", ret);
> > > >>                  meta->rx_hash = 0; /* Used by AF_XDP as not avail signal */
> > > >> +       }
> > > >>
> > > >>          return bpf_redirect_map(&xsk, ctx->rx_queue_index, XDP_PASS);
> > > >>   }
> > > >> diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c
> > > >> index 400bfe19abfe..f3ec07ccdc95 100644
> > > >> --- a/tools/testing/selftests/bpf/xdp_hw_metadata.c
> > > >> +++ b/tools/testing/selftests/bpf/xdp_hw_metadata.c
> > > >> @@ -3,6 +3,9 @@
> > > >>   /* Reference program for verifying XDP metadata on real HW. Functional test
> > > >>    * only, doesn't test the performance.
> > > >>    *
> > > >> + * BPF-prog bpf_printk info outout can be access via
> > > >> + * /sys/kernel/debug/tracing/trace_pipe
> > > >
> > > > s/outout/output/
> > > >
> > >
> > > Fixed in V3
> > >
> > > > But let's maybe drop it? If you want to make it more usable, let's
> > > > have a separate patch to enable tracing and periodically dump it to
> > > > the console instead (as previously discussed).
> > >
> > > Cat'ing /sys/kernel/debug/tracing/trace_pipe work for me regardless of
> > > setting in
> > > /sys/kernel/debug/tracing/events/bpf_trace/bpf_trace_printk/enable
> > >
> > > We likely need a followup patch that adds a BPF config switch that can
> > > disable bpf_printk calls, because this adds overhead and thus affects
> > > the timestamps.
> >
> > No. This is by design.
> > Do not use bpf_printk* in production.
>
> But that's not for the production? xdp_hw_metadata is a small tool to
> verify that the metadata being dumped is correct (during the
> development).
> We have a proper (less verbose) selftest in
> {progs,prog_tests}/xdp_metadata.c (over veth).
> This xdp_hw_metadata was supposed to be used for running it against
> the real hardware, so having as much debugging at hand as possible
> seems helpful? (at least it was helpful to me when playing with mlx4)

The only use of bpf_printk is for debugging of bpf progs themselves.
It should not be used in any tool.

  reply	other threads:[~2023-03-22 19:17 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-21 13:47 [xdp-hints] [PATCH bpf-next V2 0/6] XDP-hints kfuncs for Intel driver igc Jesper Dangaard Brouer
2023-03-21 13:47 ` [xdp-hints] [PATCH bpf-next V2 1/6] igc: enable and fix RX hash usage by netstack Jesper Dangaard Brouer
2023-03-21 13:47 ` [xdp-hints] [PATCH bpf-next V2 2/6] selftests/bpf: xdp_hw_metadata track more timestamps Jesper Dangaard Brouer
2023-03-21 13:47 ` [xdp-hints] [PATCH bpf-next V2 3/6] selftests/bpf: xdp_hw_metadata RX hash return code info Jesper Dangaard Brouer
2023-03-21 18:47   ` [xdp-hints] " Stanislav Fomichev
2023-03-22 16:05     ` Jesper Dangaard Brouer
2023-03-22 16:07       ` Alexei Starovoitov
2023-03-22 19:00         ` Stanislav Fomichev
2023-03-22 19:17           ` Alexei Starovoitov [this message]
2023-03-22 19:22             ` Stanislav Fomichev
2023-03-22 19:30               ` Alexei Starovoitov
2023-03-22 19:33                 ` Stanislav Fomichev
2023-03-23  8:51                   ` Jesper Dangaard Brouer
2023-03-23 17:35                     ` Alexei Starovoitov
2023-03-23 17:47                       ` Stanislav Fomichev
2023-03-24 12:14                         ` Jesper Dangaard Brouer
2023-03-24 19:40                           ` Stanislav Fomichev
2023-03-21 13:47 ` [xdp-hints] [PATCH bpf-next V2 4/6] igc: add igc_xdp_buff wrapper for xdp_buff in driver Jesper Dangaard Brouer
2023-03-21 13:47 ` [xdp-hints] [PATCH bpf-next V2 5/6] igc: add XDP hints kfuncs for RX timestamp Jesper Dangaard Brouer
2023-03-21 13:47 ` [xdp-hints] [PATCH bpf-next V2 6/6] igc: add XDP hints kfuncs for RX hash Jesper Dangaard Brouer

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