Timing issue with Dummynet on high kernel timer interrupt

[Luigi Rizzo]

On Fri, Nov 6, 2015 at 9:44 AM, Hans Petter Selasky <hps at selasky.org> wrote:
> On 11/06/15 01:08, Rasool Al-Saadi wrote:
>>
>>
>> On Thursday, 5 November 2015 8:53 PM, Hans Petter Selasky wrote:
>>>
>>>
>>> On 11/05/15 00:44, Rasool Al-Saadi wrote:
...
>> Removing C_HARDCLOCK reduces the problem but doesn't  solve it completely.
>> However, removing  C_DIRECT_EXEC  instead solves the problem (but
>> occasionally  very small spike(s) appears in high hz values).
>> I mentioned in my first email that removing these flags makes the issue to
>> disappear. But what the effects of removing these flags? If it cause timing
>> issue to Dummynet, why we should use them?
>>
>
> Hi,
>
> The C_DIRECT_EXEC flag reduces task switching overhead, that you don't have
> to wakeup a thread to wakeup the dummynet worker thread. It affects timing.

Hans,
thanks for the explanation.

Can you clarify the behaviour of C_DIRECT_EXEC ?
Does this mean that the task is run within some common
thread instead of a dedicated one ?

If so, for this type of task (dummynet may run at high rate
and use a significant amount of cpu time) it may be a good
idea to remove C_DIRECT_EXEC altogether.

cheers
luigi