| Message ID | 20200819092811.GA2420@lore-desk |
|---|---|
| State | RFC |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | xdp generic default option | expand |
Lorenzo Bianconi <lorenzo@kernel.org> writes: > Hi Andrii, > > working on xdp multi-buff I figured out now xdp generic is the default choice > if not specified by userspace. In particular after commit 7f0a838254bd > ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running > the command below, XDP will run in generic mode even if the underlay driver > support XDP in native mode: > > $ip link set dev eth0 xdp obj prog.o > $ip link show dev eth0 > 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT > group default qlen 1024 > link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff > prog/xdp id 1 tag 3b185187f1855c4c jited Yeah, defaulting to xdpgeneric is not a good idea (and a change in behaviour; I get native mode on the same command on a 5.8 kernel)... -Toke
On Wed, 19 Aug 2020 11:28:11 +0200 Lorenzo Bianconi wrote: > Hi Andrii, > > working on xdp multi-buff I figured out now xdp generic is the default choice > if not specified by userspace. In particular after commit 7f0a838254bd > ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running > the command below, XDP will run in generic mode even if the underlay driver > support XDP in native mode: Make me wonder if bpf/test_offload.py was ever run on those changes :/
On Wed, Aug 19, 2020 at 2:29 AM Lorenzo Bianconi <lorenzo@kernel.org> wrote: > > Hi Andrii, > > working on xdp multi-buff I figured out now xdp generic is the default choice > if not specified by userspace. In particular after commit 7f0a838254bd > ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running > the command below, XDP will run in generic mode even if the underlay driver > support XDP in native mode: > > $ip link set dev eth0 xdp obj prog.o > $ip link show dev eth0 > 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT > group default qlen 1024 > link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff > prog/xdp id 1 tag 3b185187f1855c4c jited > > Is it better to use xdpdrv as default choice if not specified by userspace? > doing something like: > > diff --git a/net/core/dev.c b/net/core/dev.c > index a00aa737ce29..1f85880ee412 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags) > { > if (flags & XDP_FLAGS_HW_MODE) > return XDP_MODE_HW; > - if (flags & XDP_FLAGS_DRV_MODE) > - return XDP_MODE_DRV; > - return XDP_MODE_SKB; > + if (flags & XDP_FLAGS_SKB_MODE) > + return XDP_MODE_SKB; > + return XDP_MODE_DRV; > } > I think the better way would be to choose XDP_MODE_DRV if ndo_bpf != NULL and XDP_MODE_SKB otherwise. That seems to be matching original behavior, no? It was not my intent to change the behavior, sorry about that. I'll post patch a bit later today. > static bpf_op_t dev_xdp_bpf_op(struct net_device *dev, enum bpf_xdp_mode mode) > > Regards, > Lorenzo
On Wed, 19 Aug 2020 13:57:51 -0700 Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > On Wed, Aug 19, 2020 at 2:29 AM Lorenzo Bianconi <lorenzo@kernel.org> wrote: > > > > Hi Andrii, > > > > working on xdp multi-buff I figured out now xdp generic is the default choice > > if not specified by userspace. In particular after commit 7f0a838254bd > > ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running > > the command below, XDP will run in generic mode even if the underlay driver > > support XDP in native mode: > > > > $ip link set dev eth0 xdp obj prog.o > > $ip link show dev eth0 > > 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT > > group default qlen 1024 > > link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff > > prog/xdp id 1 tag 3b185187f1855c4c jited > > > > Is it better to use xdpdrv as default choice if not specified by userspace? > > doing something like: > > > > diff --git a/net/core/dev.c b/net/core/dev.c > > index a00aa737ce29..1f85880ee412 100644 > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags) > > { > > if (flags & XDP_FLAGS_HW_MODE) > > return XDP_MODE_HW; > > - if (flags & XDP_FLAGS_DRV_MODE) > > - return XDP_MODE_DRV; > > - return XDP_MODE_SKB; > > + if (flags & XDP_FLAGS_SKB_MODE) > > + return XDP_MODE_SKB; > > + return XDP_MODE_DRV; > > } > > > > I think the better way would be to choose XDP_MODE_DRV if ndo_bpf != > NULL and XDP_MODE_SKB otherwise. That seems to be matching original > behavior, no? Yes, but this silent fallback to XDP_MODE_SKB (generic-XDP) have cause a lot of support issues in the past. I wish we could change it. We already changed all the samples/bpf/ to ask for XDP_FLAGS_DRV_MODE, so they behave this way. d50ecc46d18f ("samples/bpf: Attach XDP programs in driver mode by default") https://git.kernel.org/torvalds/c/d50ecc46d18fa > It was not my intent to change the behavior, sorry about that. I'll > post patch a bit later today.
On 8/20/20 2:25 AM, Jesper Dangaard Brouer wrote: >>> diff --git a/net/core/dev.c b/net/core/dev.c >>> index a00aa737ce29..1f85880ee412 100644 >>> --- a/net/core/dev.c >>> +++ b/net/core/dev.c >>> @@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags) >>> { >>> if (flags & XDP_FLAGS_HW_MODE) >>> return XDP_MODE_HW; >>> - if (flags & XDP_FLAGS_DRV_MODE) >>> - return XDP_MODE_DRV; >>> - return XDP_MODE_SKB; >>> + if (flags & XDP_FLAGS_SKB_MODE) >>> + return XDP_MODE_SKB; >>> + return XDP_MODE_DRV; >>> } >>> >> >> I think the better way would be to choose XDP_MODE_DRV if ndo_bpf != >> NULL and XDP_MODE_SKB otherwise. That seems to be matching original >> behavior, no? > > Yes, but this silent fallback to XDP_MODE_SKB (generic-XDP) have > cause a lot of support issues in the past. I wish we could change it. > We already changed all the samples/bpf/ to ask for XDP_FLAGS_DRV_MODE, > so they behave this way. > I would prefer the flags check in Lorenzo's proposed patch which is an explicit opt in to the SKB mode.
diff --git a/net/core/dev.c b/net/core/dev.c index a00aa737ce29..1f85880ee412 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags) { if (flags & XDP_FLAGS_HW_MODE) return XDP_MODE_HW; - if (flags & XDP_FLAGS_DRV_MODE) - return XDP_MODE_DRV; - return XDP_MODE_SKB; + if (flags & XDP_FLAGS_SKB_MODE) + return XDP_MODE_SKB; + return XDP_MODE_DRV; } static bpf_op_t dev_xdp_bpf_op(struct net_device *dev, enum bpf_xdp_mode mode)
Hi Andrii, working on xdp multi-buff I figured out now xdp generic is the default choice if not specified by userspace. In particular after commit 7f0a838254bd ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running the command below, XDP will run in generic mode even if the underlay driver support XDP in native mode: $ip link set dev eth0 xdp obj prog.o $ip link show dev eth0 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT group default qlen 1024 link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff prog/xdp id 1 tag 3b185187f1855c4c jited Is it better to use xdpdrv as default choice if not specified by userspace? doing something like: Regards, Lorenzo