Re: XDP performance regression due to CONFIG_RETPOLINE Spectre V2

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On Tue, Apr 17, 2018 at 09:07:01AM +0200, Jesper Dangaard Brouer wrote:
> > > number should improve more).  
> > 
> > What is the number for the otherwise comparable setup without repolines?
> 
> Approx 12 Mpps.
> 
> You forgot to handle the dma_direct_mapping_error() case, which still
> used the retpoline in the above 8.9 Mpps measurement, I fixed it up and
> performance increased to 9.6 Mpps.
> 
> Notice, in this test there are still two retpoline/indirect-calls
> left.  The net_device->ndo_xdp_xmit and the invocation of the XDP BPF
> prog.

But that seems like a pretty clear indicator that we want the fast path
direct mapping.  I'll try to find some time over the next weeks to
do a cleaner version of it.



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