Re: [PATCH] net: fec: select queue depending on VLAN priority

[Stefan Agner]

On 2017-05-09 19:42, Andy Duan wrote:
> From: David Miller <davem@xxxxxxxxxxxxx> Sent: Tuesday, May 09, 2017 9:39 PM
>>To: stefan@xxxxxxxx
>>Cc: Andy Duan <fugang.duan@xxxxxxx>; andrew@xxxxxxx;
>>festevam@xxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-
>>kernel@xxxxxxxxxxxxxxx
>>Subject: Re: [PATCH] net: fec: select queue depending on VLAN priority
>>
>>From: Stefan Agner <stefan@xxxxxxxx>
>>Date: Mon,  8 May 2017 22:37:08 -0700
>>
>>> Since the addition of the multi queue code with commit 59d0f7465644
>>> ("net: fec: init multi queue date structure") the queue selection has
>>> been handelt by the default transmit queue selection implementation
>>> which tries to evenly distribute the traffic across all available
>>> queues. This selection presumes that the queues are using an equal
>>> priority, however, the queues 1 and 2 are actually of higher priority
>>> (the classification of the queues is enabled in fec_enet_enable_ring).
>>>
>>> This can lead to net scheduler warnings and continuous TX ring dumps
>>> when exercising the system with iperf.
>>>
>>> Use only queue 0 for all common traffic (no VLAN and P802.1p priority
>>> 0 and 1) and route level 2-7 through queue 1 and 2.
>>>
>>> Signed-off-by: Fugang Duan <fugang.duan@xxxxxxx>
>>> Fixes: 59d0f7465644 ("net: fec: init multi queue date structure")
>>
>>If the queues are used for prioritization, and it does not have multiple normal
>>priority level queues, multiqueue is not what the driver should have
>>implemented.
> Firstly, HW multiple queues support:
> 	- Traffic-shaping bandwidth distribution supports credit-based and
> round-robin-based policies. Either policy can be combined with
> time-based shaping.
> 	- AVB (Audio Video Bridging, IEEE 802.1Qav) features:
> 		* Credit-based bandwidth distribution policy can be combined with
> time-based shaping
> 		* AVB endpoint talker and listener support
> 		* Support for arbitration between different priority traffic (for
> example, AVB class A, AVB class B, and non-AVB)
> Round-robin-based policies:
> 	It has the same priority for three queues: In the round-robin QoS
> scheme, each queue is given an equal opportunity to transmit one
> frame. For example, if queue n has a frame to transmit, the queue
> transmits its frame. After queue n has transmitted its frame, or if
> queue n does not have a frame to transmit, queue n+1 is then allowed
> to transmit its frame, and so on.
> 
> Credit-based policies:
> 	The AVB credit based shaper acts independently, per class, to control
> the bandwidth distribution between normal traffic and time-sensitive
> traffic with respect to the total link bandwidth available.
> 	Credit based shaper conbined with time-based shaping:  
> 		- priority: ClassA queue > ClassB queue > best effort
> 		- ensure the queue bandwidth as user set based on time-based shaping
> algorithms (transmitter transmit frame from three queue in turn based
> on time-based shaping algorithms)
> 	And in real AVB case,  each streaming can be independent, and are
> fixed on related queue. Then driver level should implement
> .ndo_select_queue() to put the streaming into related queue. That is
> what the patch did.
> 
> The current driver config the three queue to credit-based policies
> (AVB), the patch seems no problem for the implementation. Do you have
> any suggestion ?
> 

I tried using the round robin mode by adding this:

+       /* Set Round-Robin policy */
+       writel(1, fep->hwp + FEC_QOS_SCHEME);

After a while I got the warning non the less:

WARNING: CPU: 0 PID: 0 at net/sched/sch_generic.c:316
dev_watchdog+0x248/0x24c
NETDEV WATCHDOG: eth0 (fec): transmit queue 2 timed out
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted
4.11.0-rc1-00058-g56d22eced8bc-dirty #377
Hardware name: Freescale i.MX7 Dual (Device Tree)
[<c02266b0>] (unwind_backtrace) from [<c0222d7c>] (show_stack+0x10/0x14)
[<c0222d7c>] (show_stack) from [<c04d4098>] (dump_stack+0x78/0x8c)
[<c04d4098>] (dump_stack) from [<c0236548>] (__warn+0xe8/0x100)
[<c0236548>] (__warn) from [<c0236598>] (warn_slowpath_fmt+0x38/0x48)
[<c0236598>] (warn_slowpath_fmt) from [<c0805904>]
(dev_watchdog+0x248/0x24c)
[<c0805904>] (dev_watchdog) from [<c028a0e8>] (call_timer_fn+0x28/0x98)
[<c028a0e8>] (call_timer_fn) from [<c028a1f8>] (expire_timers+0xa0/0xac)
[<c028a1f8>] (expire_timers) from [<c028a2a0>]
(run_timer_softirq+0x9c/0x194)
[<c028a2a0>] (run_timer_softirq) from [<c023aaf8>]
(__do_softirq+0x114/0x234)
[<c023aaf8>] (__do_softirq) from [<c023aee4>] (irq_exit+0xcc/0x108)
[<c023aee4>] (irq_exit) from [<c0279920>]
(__handle_domain_irq+0x80/0xec)
[<c0279920>] (__handle_domain_irq) from [<c0201544>]
(gic_handle_irq+0x48/0x8c)
[<c0201544>] (gic_handle_irq) from [<c0223838>] (__irq_svc+0x58/0x8c)
Exception stack(0xc1001f28 to 0xc1001f70)
1f20:                   00000001 00000000 00000000 c022fdc0 c1000000
c1003d80
1f40: c1003d34 c0e72ed0 c0bd9b04 c1001f80 00000000 00000000 00000000
c1001f78
1f60: c022048c c0220490 60000013 ffffffff
[<c0223838>] (__irq_svc) from [<c0220490>] (arch_cpu_idle+0x38/0x3c)
[<c0220490>] (arch_cpu_idle) from [<c026ec60>] (do_idle+0x170/0x204)
[<c026ec60>] (do_idle) from [<c026efac>] (cpu_startup_entry+0x18/0x1c)
[<c026efac>] (cpu_startup_entry) from [<c0e00c88>]
(start_kernel+0x394/0x3a0)
---[ end trace a474f341d40e0705 ]---
fec 30be0000.ethernet eth0: TX ring dump

I disabled the regular ring dump and only printed one line. It seems to
come up every 2 seconds, and checking cat /proc/interrupts showed that
queue 2 stayed at its last value (3562218):

 58:    3091320     GIC-0 150 Level     30be0000.ethernet
 59:    3562218     GIC-0 151 Level     30be0000.ethernet
 60:   13377922     GIC-0 152 Level     30be0000.ethernet


--
Stefan