[ovs-dev] [PATCH v12 00/11] Add offload support for sFlow
Chris Mi
cmi at nvidia.com
Wed Mar 24 09:17:41 UTC 2021
On 3/23/2021 10:24 PM, Ilya Maximets wrote:
> On 3/5/21 4:27 AM, Chris Mi wrote:
>> Hi Ilya,
>>
>> I think about your suggestion recently. But I'm still not very clear about the design.
>> Please see my reply below:
>>
>> On 3/1/2021 8:48 PM, Ilya Maximets wrote:
>>> On 3/1/21 9:30 AM, Chris Mi wrote:
>>>> Hi Simon, Ilya,
>>>>
>>>> Could I know what should we do to make progress for this patch set?
>>>> It has been posted in the community for a long time 😁
>>> In general, the way to get your patches reviewed is to review other
>>> patches. It's simply because we still have a huge review backlog
>>> (214 patches right now in patchwork and most of them needs review)
>>> and bugfixes usually has a bit higher priority. By reviewing other
>>> patches you're reducing amount of work for maintainers so they can
>>> get to your patches faster.
>> OK, I see.
>>> For the series and comments from Eelco:
>>> I didn't read the patches carefully, only a quick glance, but I still
>>> do not understand why we need a separate thread to poll psample events.
>>> Why can't we just allow usual handler threads to do that?
>> I'm not sure if you are aware of that the psample netlink is different from the ovs
>> netlink. Without offload, kernel sends missed packet and sFlow packet to userspace
>> using the same netlink 'ovs_packet_family'. So they can use the same handler thread.
>> But in order to offload sFlow action, we use psample kernel module to send sampled
>> packets from kernel to userspace. The format for ovs netlink message and psample
>> netlink messages are different.
> Hi. Sorry for late reply.
>
> Yes, I understand that message format is different, but it doesn't really
> matter. All the message-specific handling and parsing should happen
> inside the netdev_offload_tc_recv(). This function should have a prototype
> similar to dpif_netlink_recv(), i.e. it should receive a pointer to the
> struct dpif_upcall from the caller and fill it with data. Maybe other
> type of a generic data structure if it's really not possible to construct
> struct dpif_upcall.
>
>
>>> From the
>>> architecture perspective it's not a good thing to call ofproto code
>>> from the offload-provider. This introduces lots of complications
>>> and might cause lots of issues in the future.
>>>
>>> I'd say that design should look like this:
>>>
>>> handler thread ->
>>> dpif_recv() ->
>>> dpif_netlink_recv() ->
>>> netdev_offload_recv() ->
>>> netdev_offload_tc_recv() ->
>>> nl_sock_recv()
>> In order to use the handler thread, I'm not sure if we should add psample socket
>> fd to every handler's epoll_fd. If we should do that, we should consider how to
>> differentiate if the event comes from ovs or psample netlink. Maybe we should
>> allocate a special port number for psample and assign it to event.data.u32.
>> Anyway, that's the details. If this is the right direction, I'll think about it.
>>> Last three calls should be implemented.
>>>
>>> The better version of this will be to throw away dpif part from
>>> above call chain and make it:
>>>
>>> handler thread ->
>>> netdev_offload_recv() ->
>>> netdev_offload_tc_recv() ->
>>> nl_sock_recv()
>> If we throw away dpif part, maybe we have to write some duplicate epoll code
>> for psample only. And we can't block in nl_sock_recv(). Maybe we have to add
>> psample socket fd to every handler's epoll_fd. So we have to change the dpif
>> somehow.
> There is no need to implement any epoll_fd logic for psample.
> You may only use handler with handler_id == 0. Only this handler will receive
> psample upcalls. netdev_offload_recv_wait() should be implemented similar
> to how dpif_netlink_recv_wait() implemented for windows case, i.e. it will
> call nl_sock_wait(nl_sock, POLLIN) for the psample netlink socket.
> There is no need to block and you're never blocking anywhere because your're
> calling nl_sock_recv(..., wait = false) which will use MSG_DONTWAIT while
> actually receiving a message.
Hi Ilya,
With this new design, the code will be changed greatly. I'm not
unwilling to change it.
The effort is not small. So before I start, I want to make sure that it
is feasible.
Yes, we won't block in nl_sock_recv(), but the handler thread will be
blocked in poll_block().
If any of the vport netlink socket is readable , it will be waken up by
kernel. If we don't use
epoll_ctl to add the psample netlink socket to the handler's epoll fd,
we can't receive the
psample packet as soon as possible. That means we can only receive the
sampled packet
when there is a miss upcall.
I added some debug message in ovs epoll code and got above conclusion.
But I'm not
the expert of the epoll API, so I'm not sure if I missed anything.
Thanks,
Chris
>
> So, there should be several call chains:
>
> 1. Init.
>
> open_dpif_backer/type_run() ->
> netdev_offload_recv_set() ->
> netdev_offload_tc_recv_set(enabled) ->
> if (enable)
> psample_sock = nl_sock_create(...);
> else
> close(psample_sock);
>
> 2. Wait.
>
> udpif_upcall_handler() ->
> netdev_offload_recv_wait() ->
> netdev_offload_tc_recv_wait() ->
> if (handler_id == 0)
> nl_sock_wait(psample_sock, POLLIN);
>
> 3. Receive.
>
> udpif_upcall_handler() ->
> recv_upcalls() ->
> netdev_offload_recv() ->
> | netdev_offload_tc_recv(..., struct dpif_upcall *upcall) ->
> | if (handler_id == 0)
> | nl_sock_recv(psample_socket, ..., wait = false);
> | *upcall = <received data>;
> upcall_receive()
> process_upcall() ->
> dpif_sflow_received()
>
> 4. Deinit.
>
> close_dpif_backer() ->
> netdev_offload_recv_set(enable = false);
>
>
> Does that look more clear?
>
>> I don't know if I understand your suggestion correctly. Or I missed anything
>> So if you have time, could you please elaborate?
>>
>> Thanks,
>> Chris
>>> This way we could avoid touching dpif-netdev and still have psample
>>> offloading for the case where netdev-offload-tc is used from the
>>> userspace datapath.
>>>
>>> Above architecture also implies implementation of:
>>> - netdev_offload_recv_wait()
>>> - netdev_offload_recv_purge()
>>> - and the netdev_offload_tc_* counterparts.
>>>
>>> Best regards, Ilya Maximets.
>>>
>>>> Thanks,
>>>> Chris
>>>>
>>>> On 2/23/2021 5:08 PM, Roi Dayan wrote:
>>>>> On 2021-01-27 8:23 AM, Chris Mi wrote:
>>>>>> This patch set adds offload support for sFlow.
>>>>>>
>>>>>> Psample is a genetlink channel for packet sampling. TC action act_sample
>>>>>> uses psample to send sampled packets to userspace.
>>>>>>
>>>>>> When offloading sample action to TC, userspace creates a unique ID to
>>>>>> map sFlow action and tunnel info and passes this ID to kernel instead
>>>>>> of the sFlow info. psample will send this ID and sampled packet to
>>>>>> userspace. Using the ID, userspace can recover the sFlow info and send
>>>>>> sampled packet to the right sFlow monitoring host.
>>>>>>
>>>>>> v2-v1:
>>>>>> - Fix robot errors.
>>>>>> v3-v2:
>>>>>> - Remove Gerrit Change-Id.
>>>>>> - Add patch #9 to fix older kernels build issue.
>>>>>> - Add travis test result.
>>>>>> v4-v3:
>>>>>> - Fix offload issue when sampling rate is 1.
>>>>>> v5-v4:
>>>>>> - Move polling thread from ofproto to netdev-offload-tc.
>>>>>> v6-v5:
>>>>>> - Rebase.
>>>>>> - Add GitHub Actions test result.
>>>>>> v7-v6:
>>>>>> - Remove Gerrit Change-Id.
>>>>>> - Fix "ERROR: Inappropriate spacing around cast"
>>>>>> v8-v7
>>>>>> - Address Eelco Chaudron's comment for patch #11.
>>>>>> v9-v8
>>>>>> - Remove sflow_len from struct dpif_sflow_attr.
>>>>>> - Log a debug message for other userspace actions.
>>>>>> v10-v9
>>>>>> - Address Eelco Chaudron's comments on v9.
>>>>>> v11-v10
>>>>>> - Fix a bracing error.
>>>>>> v12-v11
>>>>>> - Add duplicate sample group id check.
>>>>>>
>>>>>> Chris Mi (11):
>>>>>> compat: Add psample and tc sample action defines for older kernels
>>>>>> ovs-kmod-ctl: Load kernel module psample
>>>>>> dpif: Introduce register sFlow upcall callback API
>>>>>> ofproto: Add upcall callback to process sFlow packet
>>>>>> netdev-offload: Introduce register sFlow upcall callback API
>>>>>> netdev-offload-tc: Implement register sFlow upcall callback API
>>>>>> dpif-netlink: Implement register sFlow upcall callback API
>>>>>> netdev-offload-tc: Introduce group ID management API
>>>>>> netdev-offload-tc: Create psample netlink socket
>>>>>> netdev-offload-tc: Add psample receive handler
>>>>>> netdev-offload-tc: Add offload support for sFlow
>>>>>>
>>>>>> include/linux/automake.mk | 4 +-
>>>>>> include/linux/psample.h | 58 +++
>>>>>> include/linux/tc_act/tc_sample.h | 25 ++
>>>>>> lib/dpif-netdev.c | 1 +
>>>>>> lib/dpif-netlink.c | 27 ++
>>>>>> lib/dpif-netlink.h | 4 +
>>>>>> lib/dpif-provider.h | 10 +
>>>>>> lib/dpif.c | 8 +
>>>>>> lib/dpif.h | 23 ++
>>>>>> lib/netdev-offload-provider.h | 3 +
>>>>>> lib/netdev-offload-tc.c | 659 ++++++++++++++++++++++++++++++-
>>>>>> lib/netdev-offload.c | 30 ++
>>>>>> lib/netdev-offload.h | 4 +
>>>>>> lib/tc.c | 61 ++-
>>>>>> lib/tc.h | 16 +-
>>>>>> ofproto/ofproto-dpif-upcall.c | 42 ++
>>>>>> utilities/ovs-kmod-ctl.in | 14 +
>>>>>> 17 files changed, 973 insertions(+), 16 deletions(-)
>>>>>> create mode 100644 include/linux/psample.h
>>>>>> create mode 100644 include/linux/tc_act/tc_sample.h
>>>>>>
>>>>> Hi Simon, Ilya,
>>>>>
>>>>> Can you help review for this series?
>>>>> do you have any comments you want us to handle?
>>>>>
>>>>> Thanks,
>>>>> Roi
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