Hi Reshma, > -----Original Message----- > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Pattan, Reshma > Sent: Friday, September 21, 2018 12:15 PM > To: long...@viettel.com.vn > Cc: dev@dpdk.org > Subject: Re: [dpdk-dev] Incorrect latencystats implementation > > Hi, > > > -----Original Message----- > > From: long...@viettel.com.vn [mailto:long...@viettel.com.vn] > > Sent: Friday, September 21, 2018 2:58 AM > > To: Pattan, Reshma <reshma.pat...@intel.com> > > Cc: dev@dpdk.org > > Subject: RE: Incorrect latencystats implementation > > > > Hi Reshma, > > > > > -----Original Message----- > > > From: reshma.pat...@intel.com [mailto:reshma.pat...@intel.com] > > > Sent: Thursday, September 20, 2018 8:09 PM > > > To: long...@viettel.com.vn > > > Cc: dev@dpdk.org > > > Subject: RE: Incorrect latencystats implementation > > > > > > > > > > > > > -----Original Message----- > > > > From: long...@viettel.com.vn [mailto:long...@viettel.com.vn] > > > > Sent: Wednesday, September 19, 2018 9:17 AM > > > > To: Pattan, Reshma <reshma.pat...@intel.com> > > > > Cc: dev@dpdk.org; Bao-Long Tran <long...@viettel.com.vn> > > > > Subject: Incorrect latencystats implementation > > > > > > > > > > > > I have submit a patch to implement the trivial fix. For the drop > > > > case I can think of 2 options. We can either clear timestamp when > > > > putting mbufs back to their pool, or change lib latencystats > > > > implementation to perform packet selection at TX callback and let RX > > > > callback add > > timestamp > > > to every packet. > > > > Both option could affect performance but I think the second option > > > > is less aggressive. > > > > > > What happens when applications drop the packets? Do they free the mbuf? > > > In such case, can application set the timestamp to 0 before freeing > > > the > > mbuf, > > > instead of making these changes in latency library.? > > > > > > > Yes, applications can set the mbuf timestamp before freeing. But in my > > opinion that would not be a clean solution. Applications should not have to > > worry about the timestamp field at all, since that is an implementation > > detail > > of the library. For simple apps, wrapping rte_pktmbuf_free() to perform > > timestamp reset could be done without much hassle, but that kind of ad-hoc > > solution would become messy for more complex ones where packets are > > dropped at different places. From a usability point of view, as an user I > > want > > the lib to provide latency measurements without me having to touch existing > > codebase other than adding codes that use the APIs. > > > > I will send a patch to add timestamp reset in rte_pktmbuf_free(). That will > be a cleaner way I think. > Let's see what other says on the patch.
That would probably affect performance. Actually, looking at rte_mbuf.h - timestamp field supposed to be valid only if PKT_RX_TIMESTAMP is set. >From other side, as I remember, PMD RX routine should reset RX flags of the >received PMD. So in theory you can rely on PKT_RX_TIMESTAMP to determine use this mbuf for latency calcs or not. Would that help? Konstantin > > Thanks, > Reshma
