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Message-ID: <02400c1a-e626-d6c3-ecfd-3b9e9e4b6988@bursov.com>
Date: Wed, 27 Oct 2021 13:31:59 +0300
From: Vitaly Bursov <vitaly@...sov.com>
To: Pavan Chebbi <pavan.chebbi@...adcom.com>,
Siva Reddy Kallam <siva.kallam@...adcom.com>
Cc: 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
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?
--
Thanks
Vitalii
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