On 2019-08-14 13:04:21 [-0400], Paul Thomas wrote:

Hi Sebastian,

Hi Paul,

The attachment is here:
https://bugzilla.kernel.org/attachment.cgi?id=284391

both traces have `printk' in it. Could you please explain what it is
doing?  It should print something to the console. The printk code in
v4.19 vs later changed and now (by default) ERR levels are printed
immediately and will cause latency spikes.
This would explain the spike but I don't understand how lazy preempt is
related here.

We don't actually need Lazy Preempt, so now that we know what the
issues is we can just turn it off in the config? However I suspect
everyone wants to get to the bottom of what's going on at this point?

There is no option for lazy-preemption. And yes, we should figure out
what is causing this.

thanks,
Paul

Sebastian