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RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V

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From: KY Srinivasan
> Sent: 16 September 2015 23:58
...
> > I think we get that.  The question is does the Remote NDIS header and
> > packet info actually need to be a part of the header data?  I would
> > argue that it probably doesn't.
> >
> > So for example in netvsc_start_xmit it looks like you are calling
> > init_page_array in order to populate a set of page buffers, but the
> > first buffer for the Remote NDIS protocol is populated as a separate
> > page and offset.  As such it doesn't seem like it necessarily needs to
> > be a part of the header data but could be maintained perhaps in a
> > separate ring buffer, or perhaps just be a separate page that you break
> > up to use for each header.
> 
> You are right; the rndis header can be built as a separate fragment and sent.
> Indeed this is what we were doing earlier - on the outgoing path we would allocate
> memory for the rndis header. My goal was to avoid this allocation on every packet being
> sent and I decided to use the headroom instead. If we can completely avoid all memory
> allocation for rndis header, it makes a significant perf difference:
...


So just preallocate the header space as a fixed buffer for each ring entry
(or tx frame).

If you allocate a fixed buffer for each ring entry you may find there are
performance gains from copying small fragments into the buffer instead
of doing whatever mapping operations are required.

	David

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Thread

[PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-09-16 18:00 +0200
  RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V Haiyang Zhang <haiyangz@microsoft.com> - 2015-09-16 18:10 +0200
    RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V David Laight <David.Laight@ACULAB.COM> - 2015-09-16 18:30 +0200
      Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V Alexander Duyck <alexander.duyck@gmail.com> - 2015-09-16 19:30 +0200
      Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V David Miller <davem@davemloft.net> - 2015-09-16 20:00 +0200
        Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-09-17 11:10 +0200
      RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V KY Srinivasan <kys@microsoft.com> - 2015-09-16 20:00 +0200
        Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V Alexander Duyck <alexander.duyck@gmail.com> - 2015-09-16 23:40 +0200
          RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V KY Srinivasan <kys@microsoft.com> - 2015-09-17 01:40 +0200
            Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V Alexander Duyck <alexander.duyck@gmail.com> - 2015-09-17 01:50 +0200
              RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V KY Srinivasan <kys@microsoft.com> - 2015-09-17 02:00 +0200
            RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V David Laight <David.Laight@ACULAB.COM> - 2015-09-17 10:40 +0200
              RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V KY Srinivasan <kys@microsoft.com> - 2015-09-17 17:20 +0200
                Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V David Miller <davem@davemloft.net> - 2015-09-17 21:00 +0200
                RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V KY Srinivasan <kys@microsoft.com> - 2015-09-17 22:00 +0200
                Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V David Miller <davem@davemloft.net> - 2015-09-17 22:20 +0200
                RE: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V KY Srinivasan <kys@microsoft.com> - 2015-09-17 23:20 +0200

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