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Date: Thu, 12 Apr 2018 16:51:23 +0200 From: Christoph Hellwig <hch@....de> To: Jesper Dangaard Brouer <brouer@...hat.com> Cc: "xdp-newbies@...r.kernel.org" <xdp-newbies@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Christoph Hellwig <hch@....de>, David Woodhouse <dwmw2@...radead.org>, William Tu <u9012063@...il.com>, Björn Töpel <bjorn.topel@...el.com>, "Karlsson, Magnus" <magnus.karlsson@...el.com>, Alexander Duyck <alexander.duyck@...il.com>, Arnaldo Carvalho de Melo <acme@...hat.com> Subject: Re: XDP performance regression due to CONFIG_RETPOLINE Spectre V2 On Thu, Apr 12, 2018 at 03:50:29PM +0200, Jesper Dangaard Brouer wrote: > --------------- > Implement support for keeping the DMA mapping through the XDP return > call, to remove RX map/unmap calls. Implement bulking for XDP > ndo_xdp_xmit and XDP return frame API. Bulking allows to perform DMA > bulking via scatter-gatter DMA calls, XDP TX need it for DMA > map+unmap. The driver RX DMA-sync (to CPU) per packet calls are harder > to mitigate (via bulk technique). Ask DMA maintainer for a common > case direct call for swiotlb DMA sync call ;-) Why do you even end up in swiotlb code? Once you bounce buffer your performance is toast anyway..
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