On 20 Nov 2019, at 17:43, Ilya Maximets wrote:
On 20.11.2019 8:35, Eelco Chaudron wrote:
On 19 Nov 2019, at 17:52, Ilya Maximets wrote:
On 19.11.2019 17:16, Eelco Chaudron wrote:
On 7 Nov 2019, at 12:36, Ilya Maximets wrote:
Until now there was only two options for XDP mode in OVS: SKB or
DRV.
i.e. 'generic XDP' or 'native XDP with zero-copy enabled'.
Devices like 'veth' interfaces in Linux supports native XDP, but
doesn't support zero-copy mode. This case can not be covered by
existing API and we have to use slower generic XDP for such
devices.
There are few more issues, e.g. TCP is not supported in generic
XDP
mode for veth interfaces due to kernel limitations, however it is
supported in native mode.
This change introduces ability to use native XDP without zero-copy
along with best-effort configuration option that enabled by
default.
In best-effort case OVS will sequentially try different modes
starting
from the fastest one and will choose the first acceptable for
current
interface. This will guarantee the best possible performance.
If user will want to choose specific mode, it's still possible by
setting the 'options:xdp-mode'.
This change additionally changes the API by renaming the
configuration
knob from 'xdpmode' to 'xdp-mode' and also renaming the modes
themselves to be more user-friendly.
The full list of currently supported modes:
* native-with-zerocopy - former DRV
* native - new one, DRV without
zero-copy
* generic - former SKB
* best-effort - new one, chooses the best
available from
3 above modes
Since 'best-effort' is a default mode, users will not need to
explicitely set 'xdp-mode' in most cases.
TCP related tests enabled back in system afxdp testsuite, because
'best-effort' will choose 'native' mode for veth interfaces
and this mode has no issues with TCP.
Patch in general looks good, two small comments inline.
Thanks for review.
The only thing that bothers me is the worse performance of the TAP
interface with the new default config. Can we somehow keep the old
behavior for TAP interfaces?
Could you check if TCP works over tap interfaces in generic mode?
For me the point is that correctness is better than performance.
I also hope that native implementation for tap will be improved
over time.
So if I understood your email chain with William correctly TCP is not
working, so I affray correctness is better than performance.
Not exactly. William didn't test the actual TAP interfaces.
I tested today with kernel vhost backed virtio-user port and it seems
to pass
TCP frames in generic mode.
The setup is following:
tap1 <-- ovs-vswitchd --> tap0 <-- testpmd --> tap2
tap1 -- tap port created by OVS (type=tap)
tap0 -- tap port, virtio-user, created by testpmd, opened by OVS with
type=afxdp
tap2 -- tap port created by testpmd (net_tap)
tap1 and tap2 are in their own network namespaces and iperf works on
them.
TCP works in this scenario regardless of xdp-mode on tap0 interface.
However, let's look at the difference before-after this patch:
PHY NIC TAP VETH
before (skb default) slow by default fast by default broken
TCP
after (best-effort) fast by default slower by default works
For the best speed before you had to configure xdp-mode for physical
NICs,
after you need to configure xdp-mode for TAPs. No much difference
from the
configuration side, but with patch applied veths are working.
So, I think this change makes sense anyway. We can think about
workaround
for TAP devices, but we still need to check more cases.
For now, I updated the 'Limitations' section with information that
generic
mode works for TAP devices and might be even faster in some cases.
I also reformatted the code for 'unspecified' and 'best-effort' modes
as
you asked and applied to master.
Best regards, Ilya Maximets.
Thanks!
//Eelco
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