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    SubjectRe: [PATCH v4 01/13] Linux RDMA Core Changes
    > > > 
    > > > It seems all Chelsio needs is to pass in a consumer index - so, how about a new
    > > > entry point? Something like void set_cq_udata(struct ib_cq *cq, struct ib_udata *udata)?
    > > >
    > >
    > > Adding a new entry point would hurt chelsio's user mode performance if
    > > if then requires 2 kernel transitions to rearm the cq.
    > No, it won't need 2 transitions - just an extra function call,
    > so it won't hurt performance - it would improve performance.
    > ib_uverbs_req_notify_cq would call
    > ib_uverbs_req_notify_cq()
    > {
    > ib_set_cq_udata(cq, udata)
    > ib_req_notify_cq(cq, cmd.solicited_only ?
    > }

    ib_set_cq_udata() would transition into the kernel to pass in the
    consumer's index. In addition, ib_req_notify_cq would also transition
    into the kernel since its not a bypass function for chelsio.

    > This way kernel consumers don't incur any overhead,
    > and in userspace users extra function call is dwarfed
    > by system call overhead.
    > > Passing in user data is sort of SOP for these sorts of verbs.
    > I don't see other examples. Where we did pass extra user data
    > is in non-data pass verbs such as create QP.
    > This is most inner tight loop in many ULPs, so we should be very careful
    > about adding code there - these things do add up.
    > See recent IRQ API update in kernel.

    Roland, do you have any comments on this? You previously indicated
    these patches were good to go once chelsio's ethernet driver gets pulled

    > > How much does passing one more param cost for kernel users?
    > Donnu. I just reviewed the code.
    > It really should be up to patch submitter to check the performance
    > effect of his patch, if there might be any.

    I've run this code with mthca and didn't notice any performance
    degradation, but I wasn't specifically measuring cq_poll overhead in a
    tight loop...

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      Last update: 2007-01-03 15:59    [W:0.023 / U:2.780 seconds]
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