On Wed, 2011-02-23 at 15:12 +0200, Avi Kivity wrote: > On 02/22/2011 08:54 PM, Alex Williamson wrote: > > This series introduces a new weight-balanced binary tree (wbtree) for > > general use. It's largely leveraged from the rbtree, copying it's > > rotate functions, while introducing different rebalance and erase > > functions. This tree is particularly useful for managing memory > > ranges, where it's desirable to have the most likely targets (the > > largest ranges) at the top of each subtree. > > > > Patches 2& 3 go on to convert the KVM memory slots to a growable > > array and make use of wbtree for efficient managment. Trying to > > exercise the worst case for this data structure, I ran netperf > > TCP_RR on an emulated rtl8139 NIC connected directly to the host > > via a tap. Both qemu-kvm and the netserver on the host were > > pinned to optimal CPUs with taskset. This series resulted in > > a 3% improvement for this test. > > > > In this case, I think most of the faults (at least after the guest was > warmed up) missed the tree completely. Except for the mmio faults for the NIC, which will traverse the entire depth of that branch of the tree for every access. > In this case a weight balanced > tree is hardly optimal (it is optimized for hits), so I think you'll see > a bigger gain from the mmio fault optimization. You'll probably see > most of the gain running mmu intensive tests with ept=0. Right, the gain expected by this test is that we're only traversing 6-7 tree nodes until we don't find a match, versus the full 32 entries of the original memslot array. So it's effectively comparing worst case scenarios for both data structures. Hopefully the followup with kernbench run with ept=0 show that there's also still a benefit in the data match scenario. The existing array ends up being nearly optimal for memory hits since it registers memory from 1M - 3.5G in slot0 and 4G - 10.5G in slot1. For the tree, we jump straight to the bigger slot. I'll run one more set of kernbench tests with the original code, just reversing slots 0&1 to see if we take much of a hit from the tree overhead. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
