linux-kernel - Re: [RFC PATCH 0/3] Weight-balanced binary tree + KVM growable memory slots using wbtree

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Message-ID: <4D6507C9.1000906@redhat.com>
Date:	Wed, 23 Feb 2011 15:12:41 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	mtosatti@...hat.com, xiaoguangrong@...fujitsu.com
Subject: Re: [RFC PATCH 0/3] Weight-balanced binary tree + KVM growable memory
 slots using wbtree

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.  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.

> Note that part of why this series is RFC is that the print_tree
> function in the last patch is debug code that generates output
> for dot.  You can copy the output to a file and run:
>
>    dot -Tpdf foo.dot>  foo.pdf
>
> to generate a nice diagram of the tree currently in use.  I'll
> follow-up with a few examples.  Thanks,
>
> Alex
>

-- 
error compiling committee.c: too many arguments to function

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