Re: [PATCHv7 bpf-next 0/3] xdp: add a new helper for dev map multicast support

On Tue, Jul 14, 2020 at 11:53:20PM +0200, Toke Høiland-Jørgensen wrote:

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David Ahern [off-list ref] writes:

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Version         | Test                                   | Native | Generic
5.8 rc1         | xdp_redirect_map       i40e->i40e      |  10.0M |   1.9M
5.8 rc1         | xdp_redirect_map       i40e->veth      |  12.7M |   1.6M
5.8 rc1 + patch | xdp_redirect_map       i40e->i40e      |  10.0M |   1.9M
5.8 rc1 + patch | xdp_redirect_map       i40e->veth      |  12.3M |   1.6M
5.8 rc1 + patch | xdp_redirect_map_multi i40e->i40e      |   7.2M |   1.5M
5.8 rc1 + patch | xdp_redirect_map_multi i40e->veth      |   8.5M |   1.3M
5.8 rc1 + patch | xdp_redirect_map_multi i40e->i40e+veth |   3.0M |  0.98M

The bpf_redirect_map_multi() is slower than bpf_redirect_map() as we loop
the arrays and do clone skb/xdpf. The native path is slower than generic
path as we send skbs by pktgen. So the result looks reasonable.

Last but not least, thanks a lot to Jiri, Eelco, Toke and Jesper for
suggestions and help on implementation.

[0] https://xdp-project.net/#Handling-multicast

v7: Fix helper flag check
    Limit the *ex_map* to use DEVMAP_HASH only and update function
    dev_in_exclude_map() to get better performance.

Did it help? The performance numbers in the table above are the same as
in v6...

If there is only 1 entry in the exclude map, then the numbers should be
about the same.

I would still expect the lack of the calls to devmap_get_next_key() to
at least provide a small speedup, no? That the numbers are completely
unchanged looks a bit suspicious...

As I replied to David, I didn't re-run the test as I thought there should
no much difference as the exclude map on has 1 entry.

There should be a small speedup compared with previous patch. But as the
test system re-installed and rebooted, there will be some jitter to the
test result. It would be a little hard to observe the improvement.

Thanks
Hangbin