[dpdk-users] KNI with RTE_KNI_PREEMPT_DEFAULT=n causes CPU soft-lockup

[junlee]

We also tried to turn off the watchdog, then we got RCU stall.
INFO: rcu_sched self-detected stall on CPU

Is there any system configuration that should be made before setting
RTE_KNI_PREEMPT_DEFAULT to n?


2017-11-27 20:49 GMT+08:00 junlee <lijun422 at gmail.com>:

> Hi Jay,
>
> Thanks.
> We have read the thread before, increasing HZ to 1000 helps, but we are
> looking for latency even less than 1ms.
> The DPDK version is 17.05.
>
> The kernel preempt setting is:
> CONFIG_PREEMPT_NONE=y
> # CONFIG_PREEMPT_VOLUNTARY is not set
> # CONFIG_PREEMPT is not set
>
> Seems the watchdog/x process could not get chance to run
> when schedule_timeout_interruptible() is not called.
>
> Thanks.
> BR//Wendy
>
> 2017-11-27 20:36 GMT+08:00 Jay Rolette <rolette at infinite.io>:
>
>> That shouldn't cause soft-lockups, but IIRC, there have been KNI bugs in
>> that past that would. Probably worth checking whatever version of DPDK you
>> are running vs. the tree for relevant fixes.
>>
>> Given what you are looking into, this thread may be of interest:
>>
>> http://dpdk.org/ml/archives/dev/2015-June/018858.html
>>
>> Jay
>>
>> On Sun, Nov 26, 2017 at 7:27 PM, junlee <lijun422 at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> We are testing KNI performance and finds the
>>> schedule_timeout_interruptible
>>> causes extra latency for packets.
>>>
>>> We tried to set RTE_KNI_PREEMPT_DEFAULT=n to reduce the latency, but ends
>>> up with CPU soft-lockup.
>>>
>>> Anybody knows how to make this work?
>>>
>>> static int
>>> kni_thread_single(void *data)
>>> {
>>> struct kni_net *knet = data;
>>> int j;
>>> struct kni_dev *dev;
>>>
>>> while (!kthread_should_stop()) {
>>> down_read(&knet->kni_list_lock);
>>> for (j = 0; j < KNI_RX_LOOP_NUM; j++) {
>>> list_for_each_entry(dev, &knet->kni_list_head, list) {
>>> kni_net_rx(dev);
>>> kni_net_poll_resp(dev);
>>> }
>>> }
>>> up_read(&knet->kni_list_lock);
>>> #ifdef RTE_KNI_PREEMPT_DEFAULT
>>> /* reschedule out for a while */
>>> schedule_timeout_interruptible(
>>> usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
>>> #endif
>>> }
>>>
>>> return 0;
>>> }
>>>
>>> Thanks.
>>>
>>
>>
>