Messages in this thread | | | Date | Thu, 24 Feb 2011 12:04:36 +0200 | From | Avi Kivity <> | Subject | Re: [RFC PATCH 0/3] Weight-balanced binary tree + KVM growable memory slots using wbtree |
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On 02/23/2011 08:06 PM, Alex Williamson wrote: > 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.
That is exactly what I meant: most of the faults cause the search to fail. What we want here is to cache the success/fail result of the search so we don't do it in the first place.
> > 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.
If we optimized the linear list we'd sort it by size, descending, and limit it by the number of instantiated slots, which I think would beat the tree.
-- error compiling committee.c: too many arguments to function
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