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xdp: change ndo_xdp_xmit API to support bulking

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This patch change the API for ndo_xdp_xmit to support bulking
xdp_frames.

When kernel is compiled with CONFIG_RETPOLINE, XDP sees a huge slowdown.
Most of the slowdown is caused by DMA API indirect function calls, but
also the net_device->ndo_xdp_xmit() call.

Benchmarked patch with CONFIG_RETPOLINE, using xdp_redirect_map with
single flow/core test (CPU E5-1650 v4 @ 3.60GHz), showed
performance improved:
 for driver ixgbe: 6,042,682 pps -> 6,853,768 pps = +811,086 pps
 for driver i40e : 6,187,169 pps -> 6,724,519 pps = +537,350 pps

With frames avail as a bulk inside the driver ndo_xdp_xmit call,
further optimizations are possible, like bulk DMA-mapping for TX.

Testing without CONFIG_RETPOLINE show the same performance for
physical NIC drivers.

The virtual NIC driver tun sees a huge performance boost, as it can
avoid doing per frame producer locking, but instead amortize the
locking cost over the bulk.

V2: Fix compile errors reported by kbuild test robot <lkp@intel.com>
V4: Isolated ndo, driver changes and callers.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Jesper Dangaard Brouer 2018-05-24 16:46:12 +02:00 • committed by Alexei Starovoitov
parent 389ab7f01a
commit 735fc4054b
8 changed files with 140 additions and 65 deletions
Download patch file Download diff file Expand all files Collapse all files

29
kernel/bpf/devmap.c
View file

@ -232,24 +232,31 @@ static int bq_xmit_all(struct bpf_dtab_netdev *obj,
prefetch(xdpf);
}
for (i = 0; i < bq->count; i++) {
struct xdp_frame *xdpf = bq->q[i];
int err;
err = dev->netdev_ops->ndo_xdp_xmit(dev, xdpf);
if (err) {
drops++;
xdp_return_frame_rx_napi(xdpf);
} else {
sent++;
}
sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q);
if (sent < 0) {
sent = 0;
goto error;
}
drops = bq->count - sent;
out:
bq->count = 0;
trace_xdp_devmap_xmit(&obj->dtab->map, obj->bit,
sent, drops, bq->dev_rx, dev);
bq->dev_rx = NULL;
return 0;
error:
/* If ndo_xdp_xmit fails with an errno, no frames have been
* xmit'ed and it's our responsibility to them free all.
*/
for (i = 0; i < bq->count; i++) {
struct xdp_frame *xdpf = bq->q[i];
/* RX path under NAPI protection, can return frames faster */
xdp_return_frame_rx_napi(xdpf);
drops++;
}
goto out;
}
/* __dev_map_flush is called from xdp_do_flush_map() which _must_ be signaled