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

[junlee <lijun422@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@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@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.
>>
>
>