Okay, I will have a look at that too. Thanks! :) On Wed, Apr 20, 2016 at 11:38 PM, Joe Stringer <j...@ovn.org> wrote:
> Please don't drop the list. > > I think that you need to just investigate further, profile, > timestamp/log different pieces of the processing. One direction might > be to monitor when the actual OpenFlow requests/responses are sent > between OVS and POX. I don't think that either OVS or POX are made for > this kind of use case, so I don't have any more information than you > about where the latency is introduced. > > On 20 April 2016 at 11:28, Adil Ahmad <adilahma...@gmail.com> wrote: > > Hi, > > > > Thanks for the reply. Yes, I understand the points that you've made. So, > > currently I am able to fetch updated stats about every ~1.5 ms usually, > > after changing the line. But after about every 30ms, I experience a > 'jump', > > which means that the flow stats event callback returns after about ~50 > ms. I > > think hardware constraints come into play but I am not sure. Can you help > > explain this? > > > > Adil > > > > On Wed, Apr 20, 2016 at 11:16 PM, Joe Stringer <j...@ovn.org> wrote: > >> > >> On 19 April 2016 at 12:56, Adil Ahmad <adilahma...@gmail.com> wrote: > >> > Hi, > >> > > >> > I am trying to decrease the time that OVS takes to update its > >> > packet/byte > >> > counters. I was previously told that the line 898 of > >> > ofproto-dpif-upcall.c > >> > which is part of function udpif_validator is used to set the timer. > The > >> > line > >> > is as follows: > >> > > >> > // Original > >> > poll_timer_wait_until(start_time + MIN(ofproto_max_idle, 500)); > >> > > >> > //Changed > >> > poll_timer_wait_until(start_time + MIN(ofproto_max_idle, 1)); > >> > >> Note that this timer simply sets the typical time that the revalidator > >> thread will sleep *after finishing all of its work*, so it doesn't > >> guarantee that stats will be synchronized every 1ms. > >> > >> > I changed it to 1 and I can now get updated counters at ~1ms > frequency. > >> > However, I have noticed that after about 30 ms, there is a sudden jump > >> > and > >> > the stats handler takes a jump by about ~50ms. My controller is POX > >> > based > >> > and my timer is python datetime timer with microsecond granularity. > >> > > >> > Can anyone tell me why I see the jump? > >> > >> What do you mean by "jump"? > >> > >> All you've done is increase the consistency of stats within OVS - the > >> kernel module is more closely synchronised with the OpenFlow rules in > >> userspace. If you're fetching the stats via OpenFlow, then the main > >> thread might not be able to wake up and provide stats as quickly as > >> you want. Even if that is possible, there's still a whole host of > >> other potential pitfalls to trying to get realtime stats. > > > > >
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