On 11/12/19 10:01 AM, Joakim Zhang wrote:
>
>> -----Original Message-----
>> From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
>> Sent: 2019年11月12日 16:38
>> To: Joakim Zhang <qiangqing.zhang@xxxxxxx>; sean@xxxxxxxxxx;
>> linux-can@xxxxxxxxxxxxxxx
>> Subject: Re: Wake up issue about Flexcan driver in v5.4 kernel
>>
>> On 11/12/19 8:12 AM, Joakim Zhang wrote:
>>> I dump some info in wake up case from v5.3.10 with below change:
>>> printk("\nmailbox_num = %u, timestamp = %u, can_id = %x\n", n,
>>> *timestamp, cf->can_id);
>>
>> Keep in mind, a printk() compared to a trace_printk() will introduce bigger
>> latencies.
>
> Thanks Marc, I will learn how to use trace_printk() later as it
> cannot work at my side now.
Ok
> However, the same output without printk(), so the latencies here has
> no effect.
If printk() outputs to serial console it has a huge overhead. Further
trace_printk() is designed to have very low overhead, even when compared
to printk() not outputting to console.
[...]
>> Yes, these timestamps are all over the place. It's due to the "big" gap of 100ms
>> between the CAN frames. What's the configured bitrate of your bus?
>
> ip link set can0 up type can bitrate 1000000
With 1Mbit/s you have overruns every 65ms (worst case).
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
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