Thanks for catching this, Joel. I'm curious how we didn't notice this... I'd think there'd be a significant change in at least a few of our regression statistics. Did it not make much difference because our tests are lame, or did it make a difference but we weren't paying attention?
Steve On Tue, Aug 21, 2012 at 12:51 PM, Joel Hestness <[email protected]>wrote: > Hey everyone, > I've found a pretty major bug in the Ruby memory controller that > everyone should be aware of: > > Back when the Ruby memory controller used the Ruby event queue interface > (prior to changeset 8937:225590437eb2), the mem_bus_cycle_multiplier was > used as the number of Ruby cycles before the memory controller should by > cycled. For example, if set to 10 (the default), the memory controller > would cycle every 10 Ruby cycles, and by default the Ruby clock was set to > 2GHz, so a multiplier of 10 would mean that the memory controller has an > effective frequency of 200MHz. > > In changeset 8937:225590437eb2, the memory controller was switched over > to using the gem5 event queue interface, which uses ticks for scheduling > events. Despite the change from Ruby cycles to ticks for scheduling, the > memory controller was still scheduling cycle events based on this > multiplier value, simply adding it to the current tick. Going back to our > example of a multiplier of 10, this means that the memory controller would > be cycled every 10 ticks or at an effective frequency of 100GHz if a tick > is 1ps. > > I wanted to give everyone a head's up about this bug, since I haven't > seen anything on the email list previously. I'm currently working on a > fix, which I should have ready for review later today. > > Joel > > -- > Joel Hestness > PhD Student, Computer Architecture > Dept. of Computer Science, University of Wisconsin - Madison > http://www.cs.utexas.edu/~hestness > > _______________________________________________ > gem5-users mailing list > [email protected] > http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users > _______________________________________________ gem5-dev mailing list [email protected] http://m5sim.org/mailman/listinfo/gem5-dev
