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

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Date:   Wed, 15 Jul 2020 20:31:32 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     David Ahern <dsahern@...il.com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, Jiri Benc <jbenc@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>, ast@...nel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Subject: 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:
> >David Ahern <dsahern@...il.com> writes:
> >>> 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