On Tue, 28 Feb 2017 10:29:41 +0000, "Ananyev, Konstantin" <konstantin.anan...@intel.com> wrote: > > > > Hi, > > > > On Tue, 28 Feb 2017 09:05:07 +0000, "Ananyev, Konstantin" > > <konstantin.anan...@intel.com> wrote: > > > Hi everyone, > > > > > > > > > > > > > In my opinion, if we have the room in the first cache line, we > > > > > should put it there. The only argument I see against is "we > > > > > may find something more important in the future, and we won't > > > > > have room for it in the first cache line". I don't feel we > > > > > should penalize today's use cases for hypothetic future use > > > > > cases. > > > > > > > > > > > > > > > > > > > >> 2. timestamp normalization point > > > > >> inside PMD RX vs somewhere later as user needs it (extra > > > > >> function in dev_ops?). > > > > > > > > > > This point could be changed. My initial proposition tries to > > > > > provide a generic API for timestamp. Let me remind it here: > > > > > > > > > > a- the timestamp is in nanosecond > > > > > b- the reference is always the same for a given path: if the > > > > > timestamp is set in a PMD, all the packets for this PMD will > > > > > have the same reference, but for 2 different PMDs (or a sw > > > > > lib), the reference would not be the same. > > > > > > > > > > We may remove a-, and just have: > > > > > - the reference and the unit are always the same for a given > > > > > path: if the timestamp is set in a PMD, all the packets for > > > > > this PMD will have the same reference and unit, but for 2 > > > > > different PMDs (or a sw lib), they would not be the same. > > > > > > > > > > In both cases, we would need a conversion code (maybe in a > > > > > library) if the application wants to work with timestamps from > > > > > several sources. The second solution removes the normalization > > > > > code in the PMD when not needed, it is probably better. > > > > > > > > I agree. > > > > > > One question - does that mean that application would need to > > > keep a track from what PMD each particular packet came to do the > > > normalization? Konstantin > > > > I'd say yes. It does not look very difficult to do, since the mbuf > > contains the input port id. > > > > I understand that we can use mbuf->port here, but it means that we'll > introduce new implicit dependency between timestamp and port values. > From my point that introduces new implications: > 1. all PMDs that do set a timestamp would also have to set port value too. > Probably not a big deal as most of PMDs do set port value anyway right > now, > but it means it would be hard to get rid/change mbuf->port in future.
Currently, all PMDs must set m->port. If in the future we remove m->port, the applications that use it will need to store the value in a mbuf metadata, or pass it as arguments through function calls. > 2. Applications would not allowed to change mbuf->port value before > normalization is done > (from what I heard some apps do update mbuf->port to store routing > decisions). > BTW, how the app would keep track which mbufs were already normalized, > and which were not? I don't think it should be allowed to change m->port value. Applications that are doing this are responsible of what they change. > 3. In theory with eth_dev_detach() - mbuf->port value might be not valid at > the point when application > would decide to do normalization. > > So to me all that approach with delayed normalization seems unnecessary > overcomplicated. > Original one suggested by Olivier, when normalization is done in PMD at RX > look > much cleaner and more manageable. Detaching a device requires a synchronization between control and data plane, and not only for this use case. In the first solution, the normalization is partial: unit is nanosecond, but the time reference is different. So, after the discussion, I'm more convinced by the second solution. Regards, Olivier
