On Fri, 2017-10-13 at 17:09 -0700, Martin KaFai Lau wrote: > On Fri, Oct 13, 2017 at 10:08:07PM +0000, Wei Wang wrote: > > From: Wei Wang <wei...@google.com> > > > > In order to not dirty the cacheline too often, we try to only update > > dst->__use and dst->lastusetime at most once per jiffy. > > > > As dst->lastusetime is only used by ipv6 garbage collector, it should > > be good enough time resolution. > > Make sense. > > > And __use is only used in ipv6_route_seq_show() to show how many times a > > dst has been used. And as __use is not atomic_t right now, it does not > > show the precise number of usage times anyway. So we think it should be > > OK to only update it at most once per jiffy. > > If __use is only bumped HZ number of times per second and we can do ~3Mpps > now, > would __use be way off?
It would, but even nowaday such value could not be trusted, due to the cuncurrent non atomic operation used to update it. This: https://marc.info/?l=linux-netdev&m=150653252930953&w=2 was an attempt to preserve a more meaningful value for '__use', but it requires an additional cacheline. I'm fine with either options. Paolo
