30/10/2020 13:41, Jerin Jacob: > On Thu, Oct 29, 2020 at 5:22 PM Slava Ovsiienko <viachesl...@nvidia.com> > wrote: > > From: Andrew Rybchenko <andrew.rybche...@oktetlabs.ru> > > > > Just five cents - exporting the offset (making it global) might have side > > effect impacting the performance. > > I agree with Slava. The offset value should be stored in the PMD structure. > IMO, We can have an ethdev API to get the offset and store it in PMD's > fastpath structures in the slow path > to use in fastpath. > > > Offset might be located in some memory sharing the cacheline with some > > other variables. > > If these variables are writable and are being updated frequently - we might > > get the cache contention. > > I'd prefer to keep all dynamic offsets In the PMD and entirely control > > memory allocation > > attributes for these ones. Hence, exporting is OK, but practical usage in > > datapath is questionable.
Yes this is a major design point: the field offsets are preferably stored in a hot cache line which depends on the driver, library or application context.
