On Mon, Jul 23, 2018 at 11:58:23AM +0530, Anshuman Khandual wrote: > 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 ? You want to test IOPS with lots of small writes and using raw ramdisk on host. -- MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
