On Fri, Jan 25, 2019 at 02:51:12PM -0800, Paul E. McKenney wrote: > > > > > > So no more than (say) 100 milliseconds? > > > > Depends on RLIMIT_MEMLOCK and on how hard userspace is trying to make > > things slow, I guess - if userspace manages to create a hashtable, > > with a few dozen megabytes in size, with worst-case assignment of > > elements to buckets (everything in a single bucket), every lookup call > > on that bucket becomes a linked list traversal through a list that > > must be stored in main memory because it's too big for the CPU caches. > > I don't know into how much time that translates. > > So perhaps you have a candidate BPF program for the RCU CPU stall warning > challenge, then. ;-)
I'd like to see one that can defeat jhash + random seed.
