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| author | Toke Høiland-Jørgensen <toke@redhat.com> | 2019-12-16 12:07:42 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2019-12-16 07:05:38 -0800 |
| commit | d50ecc46d18fa19ccf06e0c4d2ee8a050c665e3d (patch) | |
| tree | b60ffa2c725d450b8f336af5283ddc733ba8da21 /samples/bpf/xdp_adjust_tail_user.c | |
| parent | 450278977acbf494a20367c22fbb38729772d1fc (diff) | |
| download | lwn-d50ecc46d18fa19ccf06e0c4d2ee8a050c665e3d.tar.gz lwn-d50ecc46d18fa19ccf06e0c4d2ee8a050c665e3d.zip | |
samples/bpf: Attach XDP programs in driver mode by default
When attaching XDP programs, userspace can set flags to request the attach
mode (generic/SKB mode, driver mode or hw offloaded mode). If no such flags
are requested, the kernel will attempt to attach in driver mode, and then
silently fall back to SKB mode if this fails.
The silent fallback is a major source of user confusion, as users will try
to load a program on a device without XDP support, and instead of an error
they will get the silent fallback behaviour, not notice, and then wonder
why performance is not what they were expecting.
In an attempt to combat this, let's switch all the samples to default to
explicitly requesting driver-mode attach. As part of this, ensure that all
the userspace utilities have a switch to enable SKB mode. For those that
have a switch to request driver mode, keep it but turn it into a no-op.
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: David Ahern <dsahern@gmail.com>
Link: https://lore.kernel.org/bpf/20191216110742.364456-1-toke@redhat.com
Diffstat (limited to 'samples/bpf/xdp_adjust_tail_user.c')
| -rw-r--r-- | samples/bpf/xdp_adjust_tail_user.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/samples/bpf/xdp_adjust_tail_user.c b/samples/bpf/xdp_adjust_tail_user.c index d86e9ad0356b..008789eb6ada 100644 --- a/samples/bpf/xdp_adjust_tail_user.c +++ b/samples/bpf/xdp_adjust_tail_user.c @@ -120,7 +120,7 @@ int main(int argc, char **argv) xdp_flags |= XDP_FLAGS_SKB_MODE; break; case 'N': - xdp_flags |= XDP_FLAGS_DRV_MODE; + /* default, set below */ break; case 'F': xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST; @@ -132,6 +132,9 @@ int main(int argc, char **argv) opt_flags[opt] = 0; } + if (!(xdp_flags & XDP_FLAGS_SKB_MODE)) + xdp_flags |= XDP_FLAGS_DRV_MODE; + for (i = 0; i < strlen(optstr); i++) { if (opt_flags[(unsigned int)optstr[i]]) { fprintf(stderr, "Missing argument -%c\n", optstr[i]); |