Hi Bruce, In my use case, unfortunately the tag is not hash. And the tag can be on either low or high bits, depending on configuration. I wonder if it is possible to let the user to decide which bit to mask, i.e. to add another param to rte_distributor_create to define the mask.
thx & rgds, -qinglai On Thu, Nov 6, 2014 at 3:59 PM, Bruce Richardson <bruce.richardson at intel.com > wrote: > On Thu, Nov 06, 2014 at 02:36:09PM +0200, Qinglai Xiao wrote: > > Hi Bruce, > > > > There is a subtle case in which tag values are 2 and 3, respectively. > Then these two tags cannot be distinguished. There should be a better way > so as to handle this situation. > > It's not just in that, case, it's in any case where a pair of tags differ > by > only a single bit. I've been assuming that the tag is likely to be a hash > value in most cases - given that it's only 32-bit - in which case it just > doesn't > matter which bit we chose to permanently set to 1, but if there are > scenarios > where it's likely that the low bits are used but the high ones not so, we > can > look to change which bit is set to 1. Either way, the distributor just > uses a > 31-bit tag rather than a 32-bit one. > > /Bruce > > > > > thx & > > rgds > > -qinglai > > > > -----????----- > > ???: "Thomas Monjalon" <thomas.monjalon at 6wind.com> > > ????: ?2014/?11/?6 12:36 > > ???: "Bruce Richardson" <bruce.richardson at intel.com> > > ??: "dev at dpdk.org" <dev at dpdk.org>; "jigsaw" <jigsaw at gmail.com> > > ??: Re: [dpdk-dev] [PATCH] Add user defined tag calculation callback > tolibrte_distributor. > > > > 2014-11-06 09:22, Bruce Richardson: > > > On Wed, Nov 05, 2014 at 07:24:13PM +0200, jigsaw wrote: > > > > > http://dpdk.org/browse/dpdk/tree/lib/librte_distributor/rte_distributor.c#n285 > > > > > > > > new_tag = (next_mb->hash.rss | 1); > > > > > > > > Why the logical OR is needed? > > > > > > That's needed to ensure that we never track a tag with an actual value > of zero. > > > We instead always force the low bit to be 1, so that we can use zero > as an > > > "empty" value. > > > > Bruce, could you check how this code may be better commented please? > > This discussion shows that the distributor library probably needs more > > explanations in the code or doxygen. > > > > Thanks > > -- > > Thomas >
