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    SubjectRe: [PATCH 0/1] Defer skb allocation for both mergeable buffers and big packets in virtio_net
    On Fri, 20 Nov 2009 04:39:19 pm Shirley Ma wrote:
    > Guest virtio_net receives packets from its pre-allocated vring
    > buffers, then it delivers these packets to upper layer protocols
    > as skb buffs. So it's not necessary to pre-allocate skb for each
    > mergable buffer, then frees it when it's useless.
    > This patch has deferred skb allocation when receiving packets for
    > both big packets and mergeable buffers. It reduces skb pre-allocations
    > and skb_frees.
    > Based on Mickael & Avi's suggestion. A destroy function has been created
    > to push virtio free buffs to vring for unused pages, and used page private
    > to maintain page list.
    > I didn't touch small packet skb allocation to avoid extra copies for small
    > packets.
    > This patch has tested and measured against 2.6.32-rc5 git. It is built again
    > 2.6.32-rc7 kernel. Tests have been done for small packets, big packets and
    > mergeable buffers.
    > The single netperf TCP_STREAM performance improved for host to guest.
    > It also reduces UDP packets drop rate.
    > The netperf laptop results were:
    > mtu=1500
    > netperf -H xxx -l 120
    > w/o patch w/i patch (two runs)
    > guest to host: 3336.84Mb/s 3730.14Mb/s ~ 3582.88Mb/s
    > host to guest: 3165.10Mb/s 3370.39Mb/s ~ 3407.96Mb/s


    Is this using mergeable_rx_bufs? Or just big_packets?

    I'd like to drop big packet support from our driver, but I don't know
    how many kvm hosts will not offer mergable rx bufs yet. Anthony?


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