On Tue, 19 Feb 2019 12:46:57 +0100 Daniel Borkmann <dan...@iogearbox.net> wrote:
> On 02/19/2019 11:24 AM, Jesper Dangaard Brouer wrote: > > The skb->queue_mapping already have read access, via > > __sk_buff->queue_mapping. > > > > This patch allow BPF tc qdisc clsact write access to the queue_mapping via > > tc_cls_act_is_valid_access. > > > > It is already possible to change this via TC filter action skbedit > > tc-skbedit(8). Due to the lack of TC examples, lets show one: > > > > # tc qdisc add dev ixgbe1 handle ffff: ingress > > # tc filter add dev ixgbe1 parent ffff: matchall action skbedit > > queue_mapping 5 > > # tc filter list dev ixgbe1 parent ffff: > > Using handles was in the old days, if we add examples, then lets do > something more user friendly ;) > > # tc qdisc add dev ixgbe1 clsact > # tc filter replace dev ixgbe1 ingress matchall action skbedit > queue_mapping 5 > # tc filter list dev ixgbe1 ingress > > > The most common mistake is that XPS (Transmit Packet Steering) takes > > precedence over setting skb->queue_mapping. XPS is configured per DEVICE > > via /sys/class/net/DEVICE/queues/tx-*/xps_cpus via a CPU hex mask. To > > disable set mask=00. > > > > The purpose of changing skb->queue_mapping is to influence the selection of > > the net_device "txq" (struct netdev_queue), which influence selection of > > the qdisc "root_lock" (via txq->qdisc->q.lock) and txq->_xmit_lock. When > > using the MQ qdisc the txq->qdisc points to different qdiscs and associated > > locks, and HARD_TX_LOCK (txq->_xmit_lock), allowing for CPU scalability. > > > > Due to lack of TC examples, lets show howto attach clsact BPF programs: > > > > # tc qdisc add dev ixgbe2 clsact > > # tc filter replace dev ixgbe2 egress bpf da obj XXX_kern.o sec tc_qmap2cpu > > # tc filter list dev ixgbe2 egress > > > > Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com> > > --- > > net/core/filter.c | 14 +++++++++++--- > > 1 file changed, 11 insertions(+), 3 deletions(-) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index 353735575204..d05ae8d05397 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -6238,6 +6238,7 @@ static bool tc_cls_act_is_valid_access(int off, int > > size, > > case bpf_ctx_range(struct __sk_buff, tc_classid): > > case bpf_ctx_range_till(struct __sk_buff, cb[0], cb[4]): > > case bpf_ctx_range(struct __sk_buff, tstamp): > > + case bpf_ctx_range(struct __sk_buff, queue_mapping): > > break; > > default: > > return false; > > @@ -6642,9 +6643,16 @@ static u32 bpf_convert_ctx_access(enum > > bpf_access_type type, > > break; > > > > case offsetof(struct __sk_buff, queue_mapping): > > - *insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg, > > - bpf_target_off(struct sk_buff, > > queue_mapping, 2, > > - target_size)); > > + if (type == BPF_WRITE) > > + *insn++ = BPF_STX_MEM(BPF_H, si->dst_reg, si->src_reg, > > + bpf_target_off(struct sk_buff, > > + queue_mapping, > > + 2, target_size)); > > + else > > + *insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg, > > + bpf_target_off(struct sk_buff, > > + queue_mapping, > > + 2, target_size)); > > One thing we should avoid would be to allow user to write NO_QUEUE_MAPPING > into skb->queue_mapping so we don't hit the warn in sk_tx_queue_set(), I'd > add this into the ctx rewrite here. Makes sense. I would really appreciate if you could help me out writing the needed BPF instructions, as I'm not an expert here. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
