[ovs-dev] [PATCHv2] netdev-afxdp: Add interrupt mode netdev class.

William Tu u9012063 at gmail.com
Wed Mar 4 18:09:32 UTC 2020


On Fri, Feb 28, 2020 at 12:12 AM Ilya Maximets <i.maximets at ovn.org> wrote:
>
> On 2/27/20 8:52 PM, William Tu wrote:
> > On Thu, Feb 27, 2020 at 11:10 AM William Tu <u9012063 at gmail.com> wrote:
> >>
> >> On Thu, Feb 27, 2020 at 9:54 AM Ilya Maximets <i.maximets at ovn.org> wrote:
> >>>
> >>> On 2/27/20 6:51 PM, William Tu wrote:
> >>>> On Thu, Feb 27, 2020 at 9:42 AM Ilya Maximets <i.maximets at ovn.org> wrote:
> >>>>>
> >>>>> On 2/27/20 6:30 PM, William Tu wrote:
> >>>>>> The patch adds a new netdev class 'afxdp-nonpmd' to enable afxdp
> >>>>>> interrupt mode. This is similar to 'type=afxdp', except that the
> >>>>>> is_pmd field is set to false. As a result, the packet processing
> >>>>>> is handled by main thread, not pmd thread. This avoids burning
> >>>>>> the CPU to always 100% when there is no traffic.
> >>>>>>
> >>>>>> Tested-at: https://travis-ci.org/williamtu/ovs-travis/builds/655885506
> >>>>>> Signed-off-by: William Tu <u9012063 at gmail.com>
> >>>>>> ---
> >>>>>>  NEWS                  |  3 +++
> >>>>>>  lib/netdev-afxdp.c    | 20 +++++++++++++++++++-
> >>>>>>  lib/netdev-linux.c    | 20 ++++++++++++++++++++
> >>>>>>  lib/netdev-provider.h |  1 +
> >>>>>>  lib/netdev.c          |  1 +
> >>>>>>  tests/system-afxdp.at | 23 +++++++++++++++++++++++
> >>>>>>  6 files changed, 67 insertions(+), 1 deletion(-)
> >>>>>>
> >>>>>> diff --git a/NEWS b/NEWS
> >>>>>> index f62ef1f47ea8..594c55dc11d6 100644
> >>>>>> --- a/NEWS
> >>>>>> +++ b/NEWS
> >>>>>> @@ -4,6 +4,9 @@ Post-v2.13.0
> >>>>>>     - OpenFlow:
> >>>>>>       * The OpenFlow ofp_desc/serial_num may now be configured by setting the
> >>>>>>         value of other-config:dp-sn in the Bridge table.
> >>>>>> +   - AF_XDP:
> >>>>>> +     * New netdev class 'afxdp-nonpmd' for netdev-afxdp to save CPU cycles
> >>>>>> +       by enabling interrupt mode.
> >>>>>>
> >>>>>>
> >>>>>>  v2.13.0 - 14 Feb 2020
> >>>>>> diff --git a/lib/netdev-afxdp.c b/lib/netdev-afxdp.c
> >>>>>> index 482400d8d135..cd2c7c381139 100644
> >>>>>> --- a/lib/netdev-afxdp.c
> >>>>>> +++ b/lib/netdev-afxdp.c
> >>>>>> @@ -169,6 +169,12 @@ struct netdev_afxdp_tx_lock {
> >>>>>>      );
> >>>>>>  };
> >>>>>>
> >>>>>> +static int nonpmd_cnt;  /* Number of afxdp netdevs in non-pmd mode. */
> >>>>>> +static bool
> >>>>>> +netdev_is_afxdp_nonpmd(struct netdev *netdev) {
> >>>>>> +    return netdev_get_class(netdev) == &netdev_afxdp_nonpmd_class;
> >>>>>> +}
> >>>>>> +
> >>>>>>  #ifdef HAVE_XDP_NEED_WAKEUP
> >>>>>>  static inline void
> >>>>>>  xsk_rx_wakeup_if_needed(struct xsk_umem_info *umem,
> >>>>>> @@ -1115,7 +1121,10 @@ netdev_afxdp_batch_send(struct netdev *netdev, int qid,
> >>>>>>      struct netdev_linux *dev;
> >>>>>>      int ret;
> >>>>>>
> >>>>>> -    if (concurrent_txq) {
> >>>>>> +    /* Lock is required when mixing afxdp pmd and nonpmd mode.
> >>>>>> +     * ex: one device is created 'afxdp', the other is 'afxdp-nonpmd'.
> >>>>>> +     */
> >>>>>> +    if (concurrent_txq || (nonpmd_cnt != 0)) {
> >>>>>
> >>>>> I'm confused about this change.  Are you expecting same device being
> >>>>> opened twice with different netdev type?  Database should not allow this.
> >>>>
> >>>> Not the same device.
> >>>>
> >>>> For example, dev1 opened as 'afxdp', and dev2 opened as 'afxdp-nonpmd'.
> >>>> When dev2 receives a packet and send to dev1, the main thread used by dev2
> >>>> is calling the send(), while it is possible that dev2's pmd thread is
> >>>> also calling
> >>>> send(). So need a lock here.
> >>>
> >>> But they will send to different tx queues.
> >>
> >> OK,  I think you are talking about the XPS feature (dynamic txqs).
> >> I thought XPS can only work when all between pmd threads.
> >> So adding a lock here.
> >> The patch currently doesn't work without the lock. Let me investigate more.
> >>
> > More details.
> > On my test using veth (only have 1 rxq 1 txq)
> > Somehow the main thread is assigned to use queue id  = 2, which causes segfault.
>
> That is very strange...
> Could you, please, share your test setup?  I'll try to reproduce.
>
> Best regards, Ilya Maximets.

Sorry, somehow I miss your reply in my mailbox.
I simply tested it using two namespaces, one device as afxdp, the
other as afxdp-nonpmd.
---
# start ovs-vswitchd and ovsdb-server

ovs-vsctl -- add-br br0 -- set Bridge br0 datapath_type=netdev
ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=0xf

ip netns add at_ns0
ip link add p0 type veth peer name afxdp-p0
ip link set p0 netns at_ns0
ip link set dev afxdp-p0 up
ovs-vsctl add-port br0 afxdp-p0
ovs-vsctl -- set interface afxdp-p0 options:n_rxq=1
type="afxdp-nonpmd" options:xdp-mode=generic

ip netns exec at_ns0 sh << NS_EXEC_HEREDOC
ip addr add "10.1.1.1/24" dev p0
ip link set dev p0 up
NS_EXEC_HEREDOC

ip netns add at_ns1
ip link add p1 type veth peer name afxdp-p1
ip link set p1 netns at_ns1
ip link set dev afxdp-p1 up
ovs-vsctl add-port br0 afxdp-p1 -- \
               set interface afxdp-p1 type="afxdp"
options:xdp-mode=generic options:n_rxq=1

ip netns exec at_ns1 sh << NS_EXEC_HEREDOC
ip addr add "10.1.1.2/24" dev p1
ip link set dev p1 up
NS_EXEC_HEREDOC

ip netns exec at_ns0 ping  -c 10 -i .2 10.1.1.2
---

It's pretty easy to reproduce the issue, ping will crash the ovs-vswitchd.

Regards,
William


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