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Message-ID: <ca16d60c-6853-f80f-99f0-0511b8ac1ef6@bursov.com>
Date: Mon, 1 Nov 2021 12:17:00 +0200
From: Vitaly Bursov <vitaly@...sov.com>
To: Pavan Chebbi <pavan.chebbi@...adcom.com>
Cc: Siva Reddy Kallam <siva.kallam@...adcom.com>,
Prashant Sreedharan <prashant@...adcom.com>,
Michael Chan <mchan@...adcom.com>,
Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: tg3 RX packet re-order in queue 0 with RSS
01.11.2021 11:10, Pavan Chebbi wrote:
> On Mon, Nov 1, 2021 at 1:50 PM Vitaly Bursov <vitaly@...sov.com> wrote:
>>
>>
>>
>> 01.11.2021 09:06, Pavan Chebbi wrote:
>>> On Fri, Oct 29, 2021 at 9:15 PM Vitaly Bursov <vitaly@...sov.com> wrote:
>>>>
>>>>
>>>>
>>>> 29.10.2021 08:04, Pavan Chebbi пишет:
>>>>> 90On Thu, Oct 28, 2021 at 9:11 PM Vitaly Bursov <vitaly@...sov.com> wrote:
>>>>>>
>>>>>>
>>>>>> 28.10.2021 10:33, Pavan Chebbi wrote:
>>>>>>> On Wed, Oct 27, 2021 at 4:02 PM Vitaly Bursov <vitaly@...sov.com> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> 27.10.2021 12:30, Pavan Chebbi wrote:
>>>>>>>>> On Wed, Sep 22, 2021 at 12:10 PM Siva Reddy Kallam
>>>>>>>>> <siva.kallam@...adcom.com> wrote:
>>>>>>>>>>
>>>>>>>>>> Thank you for reporting this. Pavan(cc'd) from Broadcom looking into this issue.
>>>>>>>>>> We will provide our feedback very soon on this.
>>>>>>>>>>
>>>>>>>>>> On Mon, Sep 20, 2021 at 6:59 PM Vitaly Bursov <vitaly@...sov.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>> Hi,
>>>>>>>>>>>
>>>>>>>>>>> We found a occassional and random (sometimes happens, sometimes not)
>>>>>>>>>>> packet re-order when NIC is involved in UDP multicast reception, which
>>>>>>>>>>> is sensitive to a packet re-order. Network capture with tcpdump
>>>>>>>>>>> sometimes shows the packet re-order, sometimes not (e.g. no re-order on
>>>>>>>>>>> a host, re-order in a container at the same time). In a pcap file
>>>>>>>>>>> re-ordered packets have a correct timestamp - delayed packet had a more
>>>>>>>>>>> earlier timestamp compared to a previous packet:
>>>>>>>>>>> 1.00s packet1
>>>>>>>>>>> 1.20s packet3
>>>>>>>>>>> 1.10s packet2
>>>>>>>>>>> 1.30s packet4
>>>>>>>>>>>
>>>>>>>>>>> There's about 300Mbps of traffic on this NIC, and server is busy
>>>>>>>>>>> (hyper-threading enabled, about 50% overall idle) with its
>>>>>>>>>>> computational application work.
>>>>>>>>>>>
>>>>>>>>>>> NIC is HPE's 4-port 331i adapter - BCM5719, in a default ring and
>>>>>>>>>>> coalescing configuration, 1 TX queue, 4 RX queues.
>>>>>>>>>>>
>>>>>>>>>>> After further investigation, I believe that there are two separate
>>>>>>>>>>> issues in tg3.c driver. Issues can be reproduced with iperf3, and
>>>>>>>>>>> unicast UDP.
>>>>>>>>>>>
>>>>>>>>>>> Here are the details of how I understand this behavior.
>>>>>>>>>>>
>>>>>>>>>>> 1. Packet re-order.
>>>>>>>>>>>
>>>>>>>>>>> Driver calls napi_schedule(&tnapi->napi) when handling the interrupt,
>>>>>>>>>>> however, sometimes it calls napi_schedule(&tp->napi[1].napi), which
>>>>>>>>>>> handles RX queue 0 too:
>>>>>>>>>>>
>>>>>>>>>>> https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/broadcom/tg3.c#L6802-L7007
>>>>>>>>>>>
>>>>>>>>>>> static int tg3_rx(struct tg3_napi *tnapi, int budget)
>>>>>>>>>>> {
>>>>>>>>>>> struct tg3 *tp = tnapi->tp;
>>>>>>>>>>>
>>>>>>>>>>> ...
>>>>>>>>>>>
>>>>>>>>>>> /* Refill RX ring(s). */
>>>>>>>>>>> if (!tg3_flag(tp, ENABLE_RSS)) {
>>>>>>>>>>> ....
>>>>>>>>>>> } else if (work_mask) {
>>>>>>>>>>> ...
>>>>>>>>>>>
>>>>>>>>>>> if (tnapi != &tp->napi[1]) {
>>>>>>>>>>> tp->rx_refill = true;
>>>>>>>>>>> napi_schedule(&tp->napi[1].napi);
>>>>>>>>>>> }
>>>>>>>>>>> }
>>>>>>>>>>> ...
>>>>>>>>>>> }
>>>>>>>>>>>
>>>>>>>>>>> From napi_schedule() code, it should schedure RX 0 traffic handling on
>>>>>>>>>>> a current CPU, which handles queues RX1-3 right now.
>>>>>>>>>>>
>>>>>>>>>>> At least two traffic flows are required - one on RX queue 0, and the
>>>>>>>>>>> other on any other queue (1-3). Re-ordering may happend only on flow
>>>>>>>>>>> from queue 0, the second flow will work fine.
>>>>>>>>>>>
>>>>>>>>>>> No idea how to fix this.
>>>>>>>>>
>>>>>>>>> In the case of RSS the actual rings for RX are from 1 to 4.
>>>>>>>>> The napi of those rings are indeed processing the packets.
>>>>>>>>> The explicit napi_schedule of napi[1] is only re-filling rx BD
>>>>>>>>> producer ring because it is shared with return rings for 1-4.
>>>>>>>>> I tried to repro this but I am not seeing the issue. If you are
>>>>>>>>> receiving packets on RX 0 then the RSS must have been disabled.
>>>>>>>>> Can you please check?
>>>>>>>>>
>>>>>>>>
>>>>>>>> # ethtool -i enp2s0f0
>>>>>>>> driver: tg3
>>>>>>>> version: 3.137
>>>>>>>> firmware-version: 5719-v1.46 NCSI v1.5.18.0
>>>>>>>> expansion-rom-version:
>>>>>>>> bus-info: 0000:02:00.0
>>>>>>>> supports-statistics: yes
>>>>>>>> supports-test: yes
>>>>>>>> supports-eeprom-access: yes
>>>>>>>> supports-register-dump: yes
>>>>>>>> supports-priv-flags: no
>>>>>>>>
>>>>>>>> # ethtool -l enp2s0f0
>>>>>>>> Channel parameters for enp2s0f0:
>>>>>>>> Pre-set maximums:
>>>>>>>> RX: 4
>>>>>>>> TX: 4
>>>>>>>> Other: 0
>>>>>>>> Combined: 0
>>>>>>>> Current hardware settings:
>>>>>>>> RX: 4
>>>>>>>> TX: 1
>>>>>>>> Other: 0
>>>>>>>> Combined: 0
>>>>>>>>
>>>>>>>> # ethtool -x enp2s0f0
>>>>>>>> RX flow hash indirection table for enp2s0f0 with 4 RX ring(s):
>>>>>>>> 0: 0 1 2 3 0 1 2 3
>>>>>>>> 8: 0 1 2 3 0 1 2 3
>>>>>>>> 16: 0 1 2 3 0 1 2 3
>>>>>>>> 24: 0 1 2 3 0 1 2 3
>>>>>>>> 32: 0 1 2 3 0 1 2 3
>>>>>>>> 40: 0 1 2 3 0 1 2 3
>>>>>>>> 48: 0 1 2 3 0 1 2 3
>>>>>>>> 56: 0 1 2 3 0 1 2 3
>>>>>>>> 64: 0 1 2 3 0 1 2 3
>>>>>>>> 72: 0 1 2 3 0 1 2 3
>>>>>>>> 80: 0 1 2 3 0 1 2 3
>>>>>>>> 88: 0 1 2 3 0 1 2 3
>>>>>>>> 96: 0 1 2 3 0 1 2 3
>>>>>>>> 104: 0 1 2 3 0 1 2 3
>>>>>>>> 112: 0 1 2 3 0 1 2 3
>>>>>>>> 120: 0 1 2 3 0 1 2 3
>>>>>>>> RSS hash key:
>>>>>>>> Operation not supported
>>>>>>>> RSS hash function:
>>>>>>>> toeplitz: on
>>>>>>>> xor: off
>>>>>>>> crc32: off
>>>>>>>>
>>>>>>>> In /proc/interrupts there are enp2s0f0-tx-0, enp2s0f0-rx-1,
>>>>>>>> enp2s0f0-rx-2, enp2s0f0-rx-3, enp2s0f0-rx-4 interrupts, all on
>>>>>>>> different CPU cores. Kernel also has "threadirqs" enabled in
>>>>>>>> command line, I didn't check if this parameter affects the issue.
>>>>>>>>
>>>>>>>> Yes, some things start with 0, and others with 1, sorry for a confusion
>>>>>>>> in terminology, what I meant:
>>>>>>>> - There are 4 RX rings/queues, I counted starting from 0, so: 0..3.
>>>>>>>> RX0 is the first queue/ring that actually receives the traffic.
>>>>>>>> RX0 is handled by enp2s0f0-rx-1 interrupt.
>>>>>>>> - These are related to (tp->napi[i]), but i is in 1..4, so the first
>>>>>>>> receiving queue relates to tp->napi[1], the second relates to
>>>>>>>> tp->napi[2], and so on. Correct?
>>>>>>>>
>>>>>>>> Suppose, tg3_rx() is called for tp->napi[2], this function most likely
>>>>>>>> calls napi_gro_receive(&tnapi->napi, skb) to further process packets in
>>>>>>>> tp->napi[2]. And, under some conditions (RSS and work_mask), it calls
>>>>>>>> napi_schedule(&tp->napi[1].napi), which schedules tp->napi[1] work
>>>>>>>> on a currect CPU, which is designated for tp->napi[2], but not for
>>>>>>>> tp->napi[1]. Correct?
>>>>>>>>
>>>>>>>> I don't understand what napi_schedule(&tp->napi[1].napi) does for the
>>>>>>>> NIC or driver, "re-filling rx BD producer ring" sounds important. I
>>>>>>>> suspect something will break badly if I simply remove it without
>>>>>>>> replacing with something more elaborate. I guess along with re-filling
>>>>>>>> rx BD producer ring it also can process incoming packets. Is it possible?
>>>>>>>>
>>>>>>>
>>>>>>> Yes, napi[1] work may be called on the napi[2]'s CPU but it generally
>>>>>>> won't process
>>>>>>> any rx packets because the producer index of napi[1] has not changed. If the
>>>>>>> producer count did change, then we get a poll from the ISR for napi[1]
>>>>>>> to process
>>>>>>> packets. So it is mostly used to re-fill rx buffers when called
>>>>>>> explicitly. However
>>>>>>> there could be a small window where the prod index is incremented but the ISR
>>>>>>> is not fired yet. It may process some small no of packets. But I don't
>>>>>>> think this
>>>>>>> should lead to a reorder problem.
>>>>>>>
>>>>>>
>>>>>> I tried to reproduce without using bridge and veth interfaces, and it seems
>>>>>> like it's not reproducible, so traffic forwarding via a bridge interface may
>>>>>> be necessary. It also does not happen if traffic load is low, but moderate
>>>>>> load is enough - e.g. two 100 Mbps streams with 130-byte packets. It's easier
>>>>>> to reproduce with a higher load.
>>>>>>
>>>>>> With about the same setup as in an original message (bridge + veth 2
>>>>>> network namespaces), irqbalance daemon stopped, if traffic flows via
>>>>>> enp2s0f0-rx-2 and enp2s0f0-rx-4, there's no reordering. enp2s0f0-rx-1
>>>>>> still gets some interrupts, but at a much lower rate compared to 2 and
>>>>>> 4.
>>>>>>
>>>>>> namespace 1:
>>>>>> # iperf3 -u -c server_ip -p 5000 -R -b 300M -t 300 -l 130
>>>>>> - - - - - - - - - - - - - - - - - - - - - - - - -
>>>>>> [ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams
>>>>>> [ 4] 0.00-300.00 sec 6.72 GBytes 192 Mbits/sec 0.008 ms 3805/55508325 (0.0069%)
>>>>>> [ 4] Sent 55508325 datagrams
>>>>>>
>>>>>> iperf Done.
>>>>>>
>>>>>> namespace 2:
>>>>>> # iperf3 -u -c server_ip -p 5001 -R -b 300M -t 300 -l 130
>>>>>> - - - - - - - - - - - - - - - - - - - - - - - - -
>>>>>> [ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams
>>>>>> [ 4] 0.00-300.00 sec 6.83 GBytes 196 Mbits/sec 0.005 ms 3873/56414001 (0.0069%)
>>>>>> [ 4] Sent 56414001 datagrams
>>>>>>
>>>>>> iperf Done.
>>>>>>
>>>>>>
>>>>>> With the same configuration but different IP address so that instead of
>>>>>> enp2s0f0-rx-4 enp2s0f0-rx-1 would be used, there is a reordering.
>>>>>>
>>>>>>
>>>>>> namespace 1 (client IP was changed):
>>>>>> # iperf3 -u -c server_ip -p 5000 -R -b 300M -t 300 -l 130
>>>>>> - - - - - - - - - - - - - - - - - - - - - - - - -
>>>>>> [ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams
>>>>>> [ 4] 0.00-300.00 sec 6.32 GBytes 181 Mbits/sec 0.007 ms 8506/52172059 (0.016%)
>>>>>> [ 4] Sent 52172059 datagrams
>>>>>> [SUM] 0.0-300.0 sec 2452 datagrams received out-of-order
>>>>>>
>>>>>> iperf Done.
>>>>>>
>>>>>> namespace 2:
>>>>>> # iperf3 -u -c server_ip -p 5001 -R -b 300M -t 300 -l 130
>>>>>> - - - - - - - - - - - - - - - - - - - - - - - - -
>>>>>> [ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams
>>>>>> [ 4] 0.00-300.00 sec 6.59 GBytes 189 Mbits/sec 0.006 ms 6302/54463973 (0.012%)
>>>>>> [ 4] Sent 54463973 datagrams
>>>>>>
>>>>>> iperf Done.
>>>>>>
>>>>>> Swapping IP addresses in these namespaces also changes the namespace exhibiting the issue,
>>>>>> it's following the IP address.
>>>>>>
>>>>>>
>>>>>> Is there something I could check to confirm that this behavior is or is not
>>>>>> related to napi_schedule(&tp->napi[1].napi) call?
>>>>>
>>>>> in the function tg3_msi_1shot() you could store the cpu assigned to
>>>>> tnapi1 (inside the struct tg3_napi)
>>>>> and then in tg3_poll_work() you can add another check after
>>>>> if (*(tnapi->rx_rcb_prod_idx) != tnapi->rx_rcb_ptr)
>>>>> something like
>>>>> if (tnapi == &tp->napi[1] && tnapi->assigned_cpu == smp_processor_id())
>>>>> only then execute tg3_rx()
>>>>>
>>>>> This may stop tnapi 1 from reading rx pkts on the current CPU from
>>>>> which refill is called.
>>>>>
>>>>
>>>> Didn't work for me, perhaps I did something wrong - if tg3_rx() is not called,
>>>> there's an infinite loop, and after I added "work_done = budget;", it still doesn't
>>>> work - traffic does not flow.
>>>>
>>>
>>> I think the easiest way is to modify the tg3_rx() calling condition
>>> like below inside
>>> tg3_poll_work() :
>>>
>>> if (*(tnapi->rx_rcb_prod_idx) != tnapi->rx_rcb_ptr) {
>>> if (tnapi != &tp->napi[1] || (tnapi == &tp->napi[1] &&
>>> !tp->rx_refill)) {
>>> work_done += tg3_rx(tnapi, budget - work_done);
>>> }
>>> }
>>>
>>> This will prevent reading rx packets when napi[1] is scheduled only for refill.
>>> Can you see if this works?
>>>
>>
>> It doesn't hang and can receive the traffic with this change, but I don't see
>> a difference. I'm suspectig that tg3_poll_work() is called again, maybe in tg3_poll_msix(),
>> and refill happens first, and then packets are processed anyway.
>>
>
> OK I see it now. Let me try this out myself. Will get back on this.
> However, can you see with your debug prints if there is any correlation
> between the time and number of prints where napi 1 is reading packets
> on unassigned CPU to the time and number of packets you received
> out of order up the stack? Do they match with each other? If not, we may be
> incorrectly suspecting napi1 here.
>
No corellation that I can see - reordered packets are received sometimes -
10000 in 300 seconds in this test, but napi messages are logged and
rate-limited at about 100000 per second. If bandwidth is very low, then
there are no messages and no reordering. Not sure if I can isolate these
events specifically.
--
Thanks
Vitalii
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