On 2016/3/15 23:37, Catalin Marinas wrote: > On Tue, Mar 15, 2016 at 10:12:11AM +0800, Zhen Lei wrote: >> 1. In swiotlb_alloc_coherent, the branch of __get_free_pages. Directly >> return vaddr on success, and pass vaddr to free_pages on failure. >> 2. So, we can directly transparent pass vaddr from __dma_free to >> swiotlb_free_coherent, keep consistent with swiotlb_alloc_coherent. >> >> This patch have no functional change, > > I don't think so. > >> but can obtain a bit performance improvement. > > Have you actually measured it? I have not run any performance testing, but reduced a line of code. So I said "a bit".
> >> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c >> index a6e757c..b2f2834 100644 >> --- a/arch/arm64/mm/dma-mapping.c >> +++ b/arch/arm64/mm/dma-mapping.c >> @@ -187,8 +187,6 @@ static void __dma_free(struct device *dev, size_t size, >> void *vaddr, dma_addr_t dma_handle, >> struct dma_attrs *attrs) >> { >> - void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle)); >> - >> size = PAGE_ALIGN(size); >> >> if (!is_device_dma_coherent(dev)) { >> @@ -196,7 +194,7 @@ static void __dma_free(struct device *dev, size_t size, >> return; >> vunmap(vaddr); >> } >> - __dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs); >> + __dma_free_coherent(dev, size, vaddr, dma_handle, attrs); >> } > > What happens when !is_device_dma_coherent(dev)? (hint: read two lines > above __dma_free_coherent). > The whole function of __dma_free as below: (nobody use swiotlb_addr except __dma_free_coherent) static void __dma_free(struct device *dev, size_t size, void *vaddr, dma_addr_t dma_handle, struct dma_attrs *attrs) { void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle)); size = PAGE_ALIGN(size); if (!is_device_dma_coherent(dev)) { if (__free_from_pool(vaddr, size)) return; vunmap(vaddr); } __dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs); }