On 07/20/2018 06:46 PM, Michael S. Tsirkin wrote: > On Fri, Jul 20, 2018 at 09:29:37AM +0530, Anshuman Khandual wrote: >> This patch series is the follow up on the discussions we had before about >> the RFC titled [RFC,V2] virtio: Add platform specific DMA API translation >> for virito devices (https://patchwork.kernel.org/patch/10417371/). There >> were suggestions about doing away with two different paths of transactions >> with the host/QEMU, first being the direct GPA and the other being the DMA >> API based translations. >> >> First patch attempts to create a direct GPA mapping based DMA operations >> structure called 'virtio_direct_dma_ops' with exact same implementation >> of the direct GPA path which virtio core currently has but just wrapped in >> a DMA API format. Virtio core must use 'virtio_direct_dma_ops' instead of >> the arch default in absence of VIRTIO_F_IOMMU_PLATFORM flag to preserve the >> existing semantics. The second patch does exactly that inside the function >> virtio_finalize_features(). The third patch removes the default direct GPA >> path from virtio core forcing it to use DMA API callbacks for all devices. >> Now with that change, every device must have a DMA operations structure >> associated with it. The fourth patch adds an additional hook which gives >> the platform an opportunity to do yet another override if required. This >> platform hook can be used on POWER Ultravisor based protected guests to >> load up SWIOTLB DMA callbacks to do the required (as discussed previously >> in the above mentioned thread how host is allowed to access only parts of >> the guest GPA range) bounce buffering into the shared memory for all I/O >> scatter gather buffers to be consumed on the host side. >> >> Please go through these patches and review whether this approach broadly >> makes sense. I will appreciate suggestions, inputs, comments regarding >> the patches or the approach in general. Thank you. > I like how patches 1-3 look. Could you test performance > with/without to see whether the extra indirection through > use of DMA ops causes a measurable slow-down? I ran this simple DD command 10 times where /dev/vda is a virtio block device of 10GB size. dd if=/dev/zero of=/dev/vda bs=8M count=1024 oflag=direct With and without patches bandwidth which has a bit wide range does not look that different from each other. Without patches =============== ---------- 1 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.95557 s, 4.4 GB/s ---------- 2 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.05176 s, 4.2 GB/s ---------- 3 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.88314 s, 4.6 GB/s ---------- 4 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.84899 s, 4.6 GB/s ---------- 5 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 5.37184 s, 1.6 GB/s ---------- 6 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.9205 s, 4.5 GB/s ---------- 7 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 6.85166 s, 1.3 GB/s ---------- 8 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.74049 s, 4.9 GB/s ---------- 9 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 6.31699 s, 1.4 GB/s ---------- 10 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.47057 s, 3.5 GB/s With patches ============ ---------- 1 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.25993 s, 3.8 GB/s ---------- 2 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.82438 s, 4.7 GB/s ---------- 3 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.93856 s, 4.4 GB/s ---------- 4 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.83405 s, 4.7 GB/s ---------- 5 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 7.50199 s, 1.1 GB/s ---------- 6 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.28742 s, 3.8 GB/s ---------- 7 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 5.74958 s, 1.5 GB/s ---------- 8 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.99149 s, 4.3 GB/s ---------- 9 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 5.67647 s, 1.5 GB/s ---------- 10 --------- 1024+0 records in 1024+0 records out 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.93957 s, 2.9 GB/s Does this look okay ? _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
