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    SubjectRe: [patch 7/11] net: Use bigrefs for net_device.refcount
    On Tue, 13 Sep 2005 09:35:14 -0700
    Ben Greear <greearb@candelatech.com> wrote:

    > Stephen Hemminger wrote:
    > > On Tue, 13 Sep 2005 09:10:12 -0700
    > > Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
    > >
    > >
    > >>The net_device has a refcnt used to keep track of it's uses.
    > >>This is used at the time of unregistering the network device
    > >>(module unloading ..) (see netdev_wait_allrefs) .
    > >>For loopback_dev , this refcnt increment/decrement is causing
    > >>unnecessary traffic on the interlink for NUMA system
    > >>affecting it's performance. This patch improves tbench numbers by 6% on a
    > >>8way x86 Xeon (x445).
    > >>
    > >
    > >
    > > Since when is bringing a network device up/down performance critical?
    >
    > We grab and drop a reference for each poll of a device, roughly.
    >
    > See dev_hold in _netif_rx_schedule(struct net_device *dev)
    > in include/netdevice.h, for instance.

    Yeah, that would be an issue, especially since the rest of that
    path is nicely per-cpu
    -
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