On Thu, 6 Dec 2018 07:37:19 -0800 Christoph Hellwig <h...@lst.de> wrote:
> Hi all, > > a while ago Jesper reported major performance regressions due to the > spectre v2 mitigations in his XDP forwarding workloads. A large part > of that is due to the DMA mapping API indirect calls. > > It turns out that the most common implementation of the DMA API is the > direct mapping case, and now that we have merged almost all duplicate > implementations of that into a single generic one is easily feasily to > direct calls for this fast path. > > This patch adds a check if we are using dma_direct_ops in each fast path > DMA operation, and just uses a direct call instead. For the XDP workload > this increases the number of packets per second from 7,438,283 to > 9,610,088, so it provides a very significant speedup. Full test report avail here: https://github.com/xdp-project/xdp-project/blob/master/areas/dma/dma01_test_hellwig_direct_dma.org > Note that the patch depends on a lot of work either queued up in the > DMA mapping tree, or still out on the list from review, so to actually > try the patch you probably want this git tree: > > > git://git.infradead.org/users/hch/misc.git dma-direct-calls > > Gitweb: > > > http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma-direct-calls > -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu