Re: Kernel 4.6.7-rt13: Intel Ethernet driver igb causes huge latencies in cyclictest

On 2016-09-23 11:40:46 [+0000], Koehrer Mathias (ETAS/ESW5) wrote:

Hi Sebastian,

Hi Mathias,

The code that is causing the long latencies seems to be the 
function "igb_watchdog_task" within igb_main.c (Line: 4386). 
This function will be called periodically.
When I do a return at the beginning of this function the additional latency is not seen.
In particular that function calls "igb_has_link" which seems to be one candidate that is
causing additional latency.
Do you have any clue how this code can be executed properly without causing the
additional latencies?

Nope. The watchdog function is invoked via schedule_work() so it should
not be blocking anything. There is no preempt disable or anything like
that. Could you narrow it down further? The igb_has_link() seems also
small and simple.

Regards

Mathias

Sebastian