[dpdk-users] occasionally ~300us delay

[Gaëtan Rivet]

Hi,

On Wed, Feb 28, 2018 at 12:03:30AM -0500, Yuliang Li wrote:
> Also, such pause happens regularly--every 0.5s.
> 
> On Wed, Feb 28, 2018 at 12:01 AM, Yuliang Li <yuliang.li at yale.edu> wrote:
> 
> > Hi all,
> >
> > I am using dpdk to generate packets. Specifically, I have a list of
> > <packet Pi, time Ti>, meaning I want to send Pi at Ti. I wait for Ti by while
> > (rte_get_tsc_cycles()<Ti). However, sometimes I see a delay of around
> > 300us of sending packets, i.e., the sending time of some Pi is around
> > Ti+300us. It looks like the program just pauses by 300us, and then resumes.
> > Does anyone know why?
> >
> > Thanks,
> 

I would reduce entropy and gather more data.

You can isolate your process (i.e. numactl), if possible not on core 0, disable
hyper-threading, disable CPU frequency scaling.

Then, running your app:

    # grep ctxt_sw /proc/$(pidof your-dpdk-app)/status

If you have context switches, then you have other tasks throwing off your measures.
The rte-intr-thread is notorious for having bad affinities and triggering context
switches, and can be used for alarms (thus, possible regular occurence).

Regards,
-- 
Gaëtan Rivet
6WIND