netdev - Re: [PATCH V2] vhost: introduce O(1) vq metadata cache

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Message-ID: <ab222583-17ac-a4fb-0547-487caa8b866d@redhat.com>
Date:   Wed, 15 Feb 2017 13:37:17 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     wexu@...hat.com, peterx@...hat.com, vkaplans@...hat.com,
        maxime.coquelin@...hat.com
Subject: Re: [PATCH V2] vhost: introduce O(1) vq metadata cache



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<jasowang@...hat.com>
> ---
> Changes from V1:
> - silent 32bit build warning

ping