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Message-ID: <be0e1e7d-272e-7f32-9626-ed4724d7fd9a@bursov.com>
Date: Mon, 1 Nov 2021 10:20:28 +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 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.
+static int tg3_cc;
+module_param(tg3_cc, int, 0644);
+MODULE_PARM_DESC(tg3_cc, "cpu check");
+
...
+ if (tnapi->assigned_cpu != smp_processor_id())
+ net_dbg_ratelimited("tg3 refill %d budget %d napi %ld cpu %d %d",
+ tp->rx_refill, budget,
+ tnapi - tp->napi, tnapi->assigned_cpu, smp_processor_id());
napi_gro_receive(&tnapi->napi, skb);
...
+ if (*(tnapi->rx_rcb_prod_idx) != tnapi->rx_rcb_ptr) {
+ if (tnapi != &tp->napi[1] || (tnapi == &tp->napi[1] && !tp->rx_refill) || (tg3_cc == 0)) {
+ work_done += tg3_rx(tnapi, budget - work_done);
+ }
+ }
with tg3_cc set to 1:
[212915.661886] net_ratelimit: 650710 callbacks suppressed
[212915.661889] tg3 refill 0 budget 64 napi 1 cpu 0 3
[212915.661890] tg3 refill 0 budget 63 napi 1 cpu 0 3
[212915.661891] tg3 refill 0 budget 62 napi 1 cpu 0 3
[212915.661892] tg3 refill 0 budget 61 napi 1 cpu 0 3
[212915.661893] tg3 refill 0 budget 60 napi 1 cpu 0 3
[212915.661915] tg3 refill 0 budget 64 napi 1 cpu 0 3
[212915.661916] tg3 refill 0 budget 63 napi 1 cpu 0 3
[212915.661917] tg3 refill 0 budget 62 napi 1 cpu 0 3
[212915.661918] tg3 refill 0 budget 61 napi 1 cpu 0 3
[212915.661919] tg3 refill 0 budget 60 napi 1 cpu 0 3
[212920.665912] net_ratelimit: 251117 callbacks suppressed
[212920.665914] tg3 refill 0 budget 64 napi 1 cpu 0 3
[212920.665915] tg3 refill 0 budget 63 napi 1 cpu 0 3
[212920.665917] tg3 refill 0 budget 62 napi 1 cpu 0 3
[212920.665918] tg3 refill 0 budget 61 napi 1 cpu 0 3
[212920.665919] tg3 refill 0 budget 60 napi 1 cpu 0 3
[212920.665932] tg3 refill 0 budget 64 napi 1 cpu 0 3
[212920.665933] tg3 refill 0 budget 63 napi 1 cpu 0 3
[212920.665935] tg3 refill 0 budget 62 napi 1 cpu 0 3
[212920.665936] tg3 refill 0 budget 61 napi 1 cpu 0 3
[212920.665937] tg3 refill 0 budget 60 napi 1 cpu 0 3
and with tg3_cc set to 0:
[213686.689867] tg3 refill 1 budget 64 napi 1 cpu 0 3
[213686.689869] tg3 refill 1 budget 63 napi 1 cpu 0 3
[213686.689870] tg3 refill 1 budget 62 napi 1 cpu 0 3
[213686.689871] tg3 refill 1 budget 61 napi 1 cpu 0 3
[213686.689872] tg3 refill 1 budget 60 napi 1 cpu 0 3
[213686.689890] tg3 refill 0 budget 64 napi 1 cpu 0 3
[213686.689891] tg3 refill 0 budget 63 napi 1 cpu 0 3
[213686.689892] tg3 refill 0 budget 62 napi 1 cpu 0 3
[213686.689893] tg3 refill 0 budget 61 napi 1 cpu 0 3
affinity:
echo 1 > /proc/irq/106/smp_affinity # enp2s0f0-rx-1
echo 2 > /proc/irq/107/smp_affinity # enp2s0f0-rx-2
echo 4 > /proc/irq/108/smp_affinity # enp2s0f0-rx-3
echo 8 > /proc/irq/109/smp_affinity # enp2s0f0-rx-4
--
Thanks
Vitalii
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