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Date: Wed, 21 Sep 2022 15:04:21 -0400
From: Etienne Champetier <champetier.etienne@...il.com>
To: Vitaly Bursov <vitaly@...sov.com>
Cc: Pavan Chebbi <pavan.chebbi@...adcom.com>,
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
Le lun. 1 nov. 2021 à 06:17, Vitaly Bursov <vitaly@...sov.com> a écrit :
>
>
>
> 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.
I'm facing the same issue, multicast packet reordering received by tg3
going to a macvlan,
tcpdump on the nic is ok, tcpdump on the macvlan show reordering.
I'm using Alma 8.6, and for me the only fix is to go to 1 RX queue.
Was there another email thread with more progress / was there a fix
outside of tg3.c for this issue ?
(looking at the git log for tg3.c I don't see anything relevant)
Thanks
Etienne
>
> --
> Thanks
> Vitalii
>
>
>
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