Re: [PATCH] arm64: mm: only initialize swiotlb when necessary

From: Jisheng Zhang
Date: Wed Jun 08 2016 - 04:06:16 EST


Dear all,

On Wed, 8 Jun 2016 15:53:46 +0800 Jisheng Zhang wrote:

> we only initialize swiotlb when swiotlb_force is true or not all system
> memory is DMA-able, this trivial optimization saves us 64MB when
> swiotlb is not necessary.

another solution is to call swiotlb_free() as ppc does. Either solution can
solve my problem. If maintainers prefer that solution, I can send a v2 patch.

Thanks,
Jisheng

>
> Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxxx>
> ---
> arch/arm64/mm/dma-mapping.c | 15 ++++++++++++++-
> arch/arm64/mm/init.c | 3 ++-
> 2 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index c566ec8..46a4157 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -19,6 +19,7 @@
>
> #include <linux/gfp.h>
> #include <linux/acpi.h>
> +#include <linux/bootmem.h>
> #include <linux/export.h>
> #include <linux/slab.h>
> #include <linux/genalloc.h>
> @@ -29,6 +30,8 @@
>
> #include <asm/cacheflush.h>
>
> +static int swiotlb __read_mostly;
> +
> static pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot,
> bool coherent)
> {
> @@ -341,6 +344,13 @@ static int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
> return ret;
> }
>
> +static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
> +{
> + if (swiotlb)
> + return swiotlb_dma_supported(hwdev, mask);
> + return 1;
> +}
> +
> static struct dma_map_ops swiotlb_dma_ops = {
> .alloc = __dma_alloc,
> .free = __dma_free,
> @@ -354,7 +364,7 @@ static struct dma_map_ops swiotlb_dma_ops = {
> .sync_single_for_device = __swiotlb_sync_single_for_device,
> .sync_sg_for_cpu = __swiotlb_sync_sg_for_cpu,
> .sync_sg_for_device = __swiotlb_sync_sg_for_device,
> - .dma_supported = swiotlb_dma_supported,
> + .dma_supported = __swiotlb_dma_supported,
> .mapping_error = swiotlb_dma_mapping_error,
> };
>
> @@ -513,6 +523,9 @@ EXPORT_SYMBOL(dummy_dma_ops);
>
> static int __init arm64_dma_init(void)
> {
> + if (swiotlb_force || max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))
> + swiotlb = 1;
> +
> return atomic_pool_init();
> }
> arch_initcall(arm64_dma_init);
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index d45f862..7d25b4d 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -403,7 +403,8 @@ static void __init free_unused_memmap(void)
> */
> void __init mem_init(void)
> {
> - swiotlb_init(1);
> + if (swiotlb_force || max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))
> + swiotlb_init(1);
>
> set_max_mapnr(pfn_to_page(max_pfn) - mem_map);
>