Timing issue with Dummynet on high kernel timer interrupt

[Hans Petter Selasky]

On 11/05/15 00:44, Rasool Al-Saadi wrote:
>
> On Wednesday, 4 November 2015 12:34 AM, Hans Petter Selasky wrote:
>> On 11/03/15 14:14, Rasool Al-Saadi wrote:
>>> Does anyone have thoughts on what we can test next to narrow down the
>> root-cause of these unusual timing jumps?
>>
>> You might also want to test the "projects/hps_head" branch, which uses a bit
>> different callout implementation.
>
> Thanks Hans for your suggestion.
> I have tried "projects/hps_head" branch and the result is better (number of spikes is less than in the master branch). However, the problem still exists on the same timer interrupt frequencies (>3000 in my case). You can see in this graph https://goo.gl/photos/C2Mqx4xhMQuzxWnz6 the RTT spikes still there.
>
> Do you have any further suggestions?
>

Hi,

If the jitter is in the xx milliseconds range, like your graph shows, my 
guess is that td_owepreemt is not set when we return from the dummynet() 
callback. See attached patch.

Else you might want to try to remove the C_HARDCLOCK flag from 
callout_reset_sbt() in ip_dummynet.c.

--HPS

-------------- next part --------------
A non-text attachment was scrubbed...
Name: ip_dummynet.c.diff
Type: text/x-patch
Size: 529 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/freebsd-net/attachments/20151105/1e28f607/attachment.bin>