Re: Performance regression 3.11 with macvlan between 2 linux guests (bisected)

On 08/21/2013 02:04 PM, Vlad Yasevich wrote:

On 08/21/2013 08:38 AM, Christian Borntraeger wrote:

quoted

Vlad,

the patch

commit 3e4f8b787370978733ca6cae452720a4f0c296b8
Author: Vlad Yasevich [off-list ref]
Date:   Tue Jun 25 16:04:22 2013 -0400

     macvtap: Perform GSO on forwarding path.

causes a severe performance regression for 2 Linux guests with virtio-net
connected via macvlan/vtap doing iperf workload. (2GBit vs. 20Gbit)

If I understand the patch correctly, we now check for gso depending on
the
macvlan features. If the underlying hardware does not support the
necessary
offloads then we will do segmentation, even if we keep the whole
traffic internal
between two guests and even if both guests supports LRO,GSO etc.
---snip---
[...]
+       features = netif_skb_features(skb) & vlan->tap_features;
+       if (netif_needs_gso(skb, features)) {
+               struct sk_buff *segs = __skb_gso_segment(skb,
features, false);
[...]

---snip---
Shouldnt we take the features of the target device or even better do
the gsoing in the
target device driver?

A corrected patch has been sent upstream.  We take into consideration
the features on the target device that the user/vm has specified.
If the VM has enabled the TSO flags, then nothing will happen to the
GSO packet.  However, if the TSO flag is off, segmentation will be
performed.

Particularly.  This commit should fix the issue:
commit a567dd6252263c8147b7269df5d03d9e31463e11
  macvtap: simplify usage of tap_features

-vlad

-vlad

quoted

Christian

FYI, the underlying HW has:

Features for eth0:
rx-checksumming: off [fixed]
tx-checksumming: off
    tx-checksum-ipv4: off [fixed]
    tx-checksum-ip-generic: off [fixed]
    tx-checksum-ipv6: off [fixed]
    tx-checksum-fcoe-crc: off [fixed]
    tx-checksum-sctp: off [fixed]
scatter-gather: off
    tx-scatter-gather: off [fixed]
    tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: off
    tx-tcp-segmentation: off [fixed]
    tx-tcp-ecn-segmentation: off [fixed]
    tx-tcp6-segmentation: off [fixed]
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: off [requested on]
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: off [fixed]
tx-vlan-offload: off [fixed]
ntuple-filters: off [fixed]
receive-hashing: off [fixed]
highdma: off [fixed]
rx-vlan-filter: on [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
tx-mpls-segmentation: off [fixed]
fcoe-mtu: off [fixed]
tx-nocache-copy: off
loopback: off [fixed]
rx-fcs: off [fixed]
rx-all: off [fixed]
tx-vlan-stag-hw-insert: off [fixed]
rx-vlan-stag-hw-parse: off [fixed]
rx-vlan-stag-filter: off [fixed]