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Date: Thu, 28 Oct 2021 18:41:13 +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
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?
--
Thanks
Vitalii
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