Several months ago, I had been looking through my old XDP hints tree[0]
to check whether some patches not directly related to hints can be sent
standalone. Roughly at the same time, Daniel appeared and asked[1] about
GRO for cpumap from that tree.
Currently, cpumap uses its own kthread which processes cpumap-redirected
frames by batches of 8, without any weighting (but with rescheduling
points). The resulting skbs get passed to the stack via
netif_receive_skb_list(), which means no GRO happens.
Even though we can't currently pass checksum status from the drivers,
in many cases GRO performs better than the listified Rx without the
aggregation, confirmed by tests.
In order to enable GRO in cpumap, we need to do the following:
* patches 1-2: decouple the GRO struct from the NAPI struct and allow
using it out of a NAPI entity within the kernel core code;
* patch 3: switch cpumap from netif_receive_skb_list() to
gro_receive_skb().
Additional improvements:
* patch 4: optimize XDP_PASS in cpumap by using arrays instead of linked
lists;
* patch 5-6: introduce and use function do get skbs from the NAPI percpu
caches by bulks, not one at a time;
* patch 7-8: use that function in veth as well and remove the one that
was now superseded by it.
My trafficgen UDP GRO tests, small frame sizes:
GRO off GRO on
baseline 2.7 N/A Mpps
patch 3 2.3 4 Mpps
patch 8 2.4 4.7 Mpps
1...3 diff -17 +48 %
1...8 diff -11 +74 %
Daniel reported from +14%[2] to +18%[3] of throughput in neper's TCP RR
tests. On my system however, the same test gave me up to +100%.
Note that there's a series from Lorenzo[4] which achieves the same, but
in a different way. During the discussions, the approach using a
standalone GRO instance was preferred over the threaded NAPI.
[0] https://github.com/alobakin/linux/tree/xdp_hints
[1] https://lore.kernel.org/bpf/cadda351-6e93-4568-ba26-21a760bf9a57@xxxxxxxxxxxxxxxx
[2] https://lore.kernel.org/bpf/merfatcdvwpx2lj4j2pahhwp4vihstpidws3jwljwazhh76xkd@t5vsh4gvk4mh
[3] https://lore.kernel.org/bpf/yzda66wro5twmzpmjoxvy4si5zvkehlmgtpi6brheek3sj73tj@o7kd6nurr3o6
[4] https://lore.kernel.org/bpf/20241130-cpumap-gro-v1-0-c1180b1b5758@xxxxxxxxxx
Alexander Lobakin (8):
net: gro: decouple GRO from the NAPI layer
net: gro: expose GRO init/cleanup to use outside of NAPI
bpf: cpumap: switch to GRO from netif_receive_skb_list()
bpf: cpumap: reuse skb array instead of a linked list to chain skbs
net: skbuff: introduce napi_skb_cache_get_bulk()
bpf: cpumap: switch to napi_skb_cache_get_bulk()
veth: use napi_skb_cache_get_bulk() instead of xdp_alloc_skb_bulk()
xdp: remove xdp_alloc_skb_bulk()
include/linux/netdevice.h | 35 ++++--
include/linux/skbuff.h | 1 +
include/net/busy_poll.h | 11 +-
include/net/gro.h | 38 ++++--
include/net/xdp.h | 1 -
drivers/net/ethernet/brocade/bna/bnad.c | 1 +
drivers/net/ethernet/cortina/gemini.c | 1 +
drivers/net/veth.c | 3 +-
drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c | 1 +
kernel/bpf/cpumap.c | 131 ++++++++++++++-------
net/core/dev.c | 79 ++++---------
net/core/gro.c | 103 ++++++++++------
net/core/skbuff.c | 62 ++++++++++
net/core/xdp.c | 10 --
14 files changed, 306 insertions(+), 171 deletions(-)
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