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    SubjectRe: 2.6.24-rc2: Network commit causes SLUB performance regression with tbench
    From
    From: Nick Piggin <nickpiggin@yahoo.com.au>
    Date: Wed, 14 Nov 2007 05:14:27 +1100

    > On Wednesday 14 November 2007 17:12, David Miller wrote:
    > > Is your test system using HIGHMEM?
    > >
    > > That's one thing the page vector in the sk_buff can do a lot,
    > > kmaps.
    >
    > No, it's an x86-64, so no highmem.

    Ok.

    > What's also interesting is that SLAB apparently doesn't have this
    > condition. The first thing that sprung to mind is that SLAB caches
    > order > 0 allocations, while SLUB does not. However if anything,
    > that should actually favour the SLUB numbers if network is avoiding
    > order > 0 allocations.
    >
    > I'm doing some oprofile runs now to see if I can get any more info.

    Here are some other things you can play around with:

    1) Monitor the values of skb->len and skb->data_len for packets
    going over loopback.

    2) Try removing NETIF_F_SG in drivers/net/loopback.c's dev->feastures
    setting.
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