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Message-ID: <ae4bd2c2-6e88-2b1c-c47d-7510ef6a8010@bursov.com>
Date: Fri, 29 Oct 2021 18:45:40 +0300
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
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 added logging instead:
+ if (tnapi->assigned_cpu != smp_processor_id())
+ net_dbg_ratelimited("tg3 napi %ld cpu %d %d",
+ tnapi - tp->napi, tnapi->assigned_cpu, smp_processor_id());
napi_gro_receive(&tnapi->napi, skb);
And with two iperf3 streams, there's a lot of messages:
[ 3242.007898] tg3 napi 1 cpu 10 48
[ 3242.007899] tg3 napi 1 cpu 10 48
[ 3242.007911] tg3 napi 1 cpu 10 48
[ 3242.007913] tg3 napi 1 cpu 10 48
[ 3247.011898] net_ratelimit: 546560 callbacks suppressed
[ 3247.011900] tg3 napi 1 cpu 10 48
[ 3247.011902] tg3 napi 1 cpu 10 48
[ 3247.011904] tg3 napi 1 cpu 10 48
[ 3247.011905] tg3 napi 1 cpu 10 48
[ 3247.011906] tg3 napi 1 cpu 10 48
[ 3247.011928] tg3 napi 1 cpu 10 48
[ 3247.011929] tg3 napi 1 cpu 10 48
[ 3247.011931] tg3 napi 1 cpu 10 48
[ 3247.011932] tg3 napi 1 cpu 10 48
[ 3247.011933] tg3 napi 1 cpu 10 48
[ 3252.015885] net_ratelimit: 539574 callbacks suppressed
[ 3252.015888] tg3 napi 1 cpu 10 48
[ 3252.015889] tg3 napi 1 cpu 10 48
[ 3252.015891] tg3 napi 1 cpu 10 48
[ 3252.015892] tg3 napi 1 cpu 10 48
cpu 10, enp2s0f0-rx-1
# cat /proc/irq/106/effective_affinity
00000000,00000000,00000400
cpu 48, enp2s0f0-rx-4
# cat /proc/irq/109/effective_affinity
00000000,00010000,00000000
Among all printed messages, there's only "napi 1".
There's also a difference in interrupt thread's CPU usage:
201570 root -51 0 0 0 0 R 64.3 0.0 1:46.91 irq/109-enp2s0f
204687 root 20 0 9628 2084 1976 R 37.5 0.0 1:04.74 iperf3
205354 root 20 0 9628 2060 1948 R 36.7 0.0 1:01.06 iperf3
201567 root -51 0 0 0 0 R 23.3 0.0 0:44.45 irq/106-enp2s0f
The sender is CPU-bound, so there's no overload on RX side with tg3
--
Thanks
Vitalii
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