Re: [dpdk-dev] Incorrect latencystats implementation

["Pattan, Reshma" <reshma.pattan@intel.com>]

Hi,

> -----Original Message-----
> From: longtb5@viettel.com.vn [mailto:longtb5@viettel.com.vn]
> Sent: Friday, September 21, 2018 2:58 AM
> To: Pattan, Reshma <reshma.pattan@intel.com>
> Cc: dev@dpdk.org
> Subject: RE: Incorrect latencystats implementation
> 
> Hi Reshma,
> 
> > -----Original Message-----
> > From: reshma.pattan@intel.com [mailto:reshma.pattan@intel.com]
> > Sent: Thursday, September 20, 2018 8:09 PM
> > To: longtb5@viettel.com.vn
> > Cc: dev@dpdk.org
> > Subject: RE: Incorrect latencystats implementation
> >
> >
> >
> > > -----Original Message-----
> > > From: longtb5@viettel.com.vn [mailto:longtb5@viettel.com.vn]
> > > Sent: Wednesday, September 19, 2018 9:17 AM
> > > To: Pattan, Reshma <reshma.pattan@intel.com>
> > > Cc: dev@dpdk.org; Bao-Long Tran <longtb5@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.

Thanks,
Reshma