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Date:   Tue, 28 Feb 2017 11:23:34 +0800
From:   Jason Wang <>
To:     "Michael S. Tsirkin" <>
Subject: Re: [PATCH V2] vhost: introduce O(1) vq metadata cache

On 2017年02月28日 02:35, Michael S. Tsirkin wrote:
> On Wed, Feb 15, 2017 at 01:37:17PM +0800, Jason Wang wrote:
>> On 2016年12月14日 17:53, Jason Wang wrote:
>>> When device IOTLB is enabled, all address translations were stored in
>>> interval tree. O(lgN) searching time could be slow for virtqueue
>>> metadata (avail, used and descriptors) since they were accessed much
>>> often than other addresses. So this patch introduces an O(1) array
>>> which points to the interval tree nodes that store the translations of
>>> vq metadata. Those array were update during vq IOTLB prefetching and
>>> were reset during each invalidation and tlb update. Each time we want
>>> to access vq metadata, this small array were queried before interval
>>> tree. This would be sufficient for static mappings but not dynamic
>>> mappings, we could do optimizations on top.
>>> Test were done with l2fwd in guest (2M hugepage):
>>>      noiommu  | before        | after
>>> tx 1.32Mpps | 1.06Mpps(82%) | 1.30Mpps(98%)
>>> rx 2.33Mpps | 1.46Mpps(63%) | 2.29Mpps(98%)
>>> We can almost reach the same performance as noiommu mode.
>>> Signed-off-by: Jason Wang<>
>>> ---
>>> Changes from V1:
>>> - silent 32bit build warning
>> ping
> Could you rebase pls?
> I pushed my tree into linux next.

Ok, will do.


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