diff options
author | Jesper Dangaard Brouer <brouer@redhat.com> | 2018-04-17 16:46:32 +0200 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2018-04-17 10:50:29 -0400 |
commit | 039930945a72d9af5ff04ae9b9e60658a52e0770 (patch) | |
tree | e92821099697576bcdcd41e9d61f561be0e6923c /include/net/xdp.h | |
parent | 60bbf7eeef10dc647430646d7fe5e3d8d132dbec (diff) | |
download | linux-039930945a72d9af5ff04ae9b9e60658a52e0770.tar.bz2 |
xdp: transition into using xdp_frame for return API
Changing API xdp_return_frame() to take struct xdp_frame as argument,
seems like a natural choice. But there are some subtle performance
details here that needs extra care, which is a deliberate choice.
When de-referencing xdp_frame on a remote CPU during DMA-TX
completion, result in the cache-line is change to "Shared"
state. Later when the page is reused for RX, then this xdp_frame
cache-line is written, which change the state to "Modified".
This situation already happens (naturally) for, virtio_net, tun and
cpumap as the xdp_frame pointer is the queued object. In tun and
cpumap, the ptr_ring is used for efficiently transferring cache-lines
(with pointers) between CPUs. Thus, the only option is to
de-referencing xdp_frame.
It is only the ixgbe driver that had an optimization, in which it can
avoid doing the de-reference of xdp_frame. The driver already have
TX-ring queue, which (in case of remote DMA-TX completion) have to be
transferred between CPUs anyhow. In this data area, we stored a
struct xdp_mem_info and a data pointer, which allowed us to avoid
de-referencing xdp_frame.
To compensate for this, a prefetchw is used for telling the cache
coherency protocol about our access pattern. My benchmarks show that
this prefetchw is enough to compensate the ixgbe driver.
V7: Adjust for commit d9314c474d4f ("i40e: add support for XDP_REDIRECT")
V8: Adjust for commit bd658dda4237 ("net/mlx5e: Separate dma base address
and offset in dma_sync call")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/xdp.h')
-rw-r--r-- | include/net/xdp.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/net/xdp.h b/include/net/xdp.h index d0ee437753dc..137ad5f9f40f 100644 --- a/include/net/xdp.h +++ b/include/net/xdp.h @@ -103,7 +103,7 @@ struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp) return xdp_frame; } -void xdp_return_frame(void *data, struct xdp_mem_info *mem); +void xdp_return_frame(struct xdp_frame *xdpf); int xdp_rxq_info_reg(struct xdp_rxq_info *xdp_rxq, struct net_device *dev, u32 queue_index); |