Memcpy and DMA transfer become slow when disable IOMMU

Hi,

I disabled the SMMU as discussed in this forum. (remove iommus = <&smmu TEGRA_SID_PCIE5>; and dma-coherent; from the device tree.)

However, I found not only transfer by dma, but also transfer by memcpy to the device memory where I disable IOMMU is really slow. Before disable IOMMU, memcpy speed was about 2.5GB/s, now it’s only 980MB/s.

Is there any way to avoid this slow performance?