Messages in this thread Patch in this message | | | Date | Fri, 21 Aug 2020 17:28:04 +0300 | From | Mike Rapoport <> | Subject | Re: [PATCH v7 1/3] dma-contiguous: provide the ability to reserve per-numa CMA |
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On Fri, Aug 21, 2020 at 11:33:53PM +1200, Barry Song wrote: > Right now, drivers like ARM SMMU are using dma_alloc_coherent() to get > coherent DMA buffers to save their command queues and page tables. As > there is only one default CMA in the whole system, SMMUs on nodes other > than node0 will get remote memory. This leads to significant latency. > > This patch provides per-numa CMA so that drivers like SMMU can get local > memory. Tests show localizing CMA can decrease dma_unmap latency much. > For instance, before this patch, SMMU on node2 has to wait for more than > 560ns for the completion of CMD_SYNC in an empty command queue; with this > patch, it needs 240ns only. > > A positive side effect of this patch would be improving performance even > further for those users who are worried about performance more than DMA > security and use iommu.passthrough=1 to skip IOMMU. With local CMA, all > drivers can get local coherent DMA buffers. > > Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com> > Cc: Christoph Hellwig <hch@lst.de> > Cc: Marek Szyprowski <m.szyprowski@samsung.com> > Cc: Will Deacon <will@kernel.org> > Cc: Robin Murphy <robin.murphy@arm.com> > Cc: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de> > Cc: Steve Capper <steve.capper@arm.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Mike Rapoport <rppt@linux.ibm.com> > Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> > --- > -v7: with respect to Will's comments > * move to use for_each_online_node > * add description if users don't specify pernuma_cma > * provide default value for CONFIG_DMA_PERNUMA_CMA > > .../admin-guide/kernel-parameters.txt | 11 ++ > include/linux/dma-contiguous.h | 6 ++ > kernel/dma/Kconfig | 11 ++ > kernel/dma/contiguous.c | 100 ++++++++++++++++-- > 4 files changed, 118 insertions(+), 10 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index bdc1f33fd3d1..c609527fc35a 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -599,6 +599,17 @@ > altogether. For more information, see > include/linux/dma-contiguous.h > > + pernuma_cma=nn[MG]
Maybe cma_pernuma or cma_pernode?
> + [ARM64,KNL] > + Sets the size of kernel per-numa memory area for > + contiguous memory allocations. A value of 0 disables > + per-numa CMA altogether. And If this option is not > + specificed, the default value is 0. > + With per-numa CMA enabled, DMA users on node nid will > + first try to allocate buffer from the pernuma area > + which is located in node nid, if the allocation fails, > + they will fallback to the global default memory area. > + > cmo_free_hint= [PPC] Format: { yes | no } > Specify whether pages are marked as being inactive > when they are freed. This is used in CMO environments > diff --git a/include/linux/dma-contiguous.h b/include/linux/dma-contiguous.h > index 03f8e98e3bcc..fe55e004f1f4 100644 > --- a/include/linux/dma-contiguous.h > +++ b/include/linux/dma-contiguous.h > @@ -171,6 +171,12 @@ static inline void dma_free_contiguous(struct device *dev, struct page *page, > > #endif > > +#ifdef CONFIG_DMA_PERNUMA_CMA > +void dma_pernuma_cma_reserve(void); > +#else > +static inline void dma_pernuma_cma_reserve(void) { } > +#endif > + > #endif > > #endif > diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig > index 847a9d1fa634..c38979d45b13 100644 > --- a/kernel/dma/Kconfig > +++ b/kernel/dma/Kconfig > @@ -118,6 +118,17 @@ config DMA_CMA > If unsure, say "n". > > if DMA_CMA > + > +config DMA_PERNUMA_CMA > + bool "Enable separate DMA Contiguous Memory Area for each NUMA Node" > + default NUMA && ARM64 > + help > + Enable this option to get pernuma CMA areas so that devices like > + ARM64 SMMU can get local memory by DMA coherent APIs. > + > + You can set the size of pernuma CMA by specifying "pernuma_cma=size" > + on the kernel's command line. > + > comment "Default contiguous memory area size:" > > config CMA_SIZE_MBYTES > diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c > index cff7e60968b9..0383c9b86715 100644 > --- a/kernel/dma/contiguous.c > +++ b/kernel/dma/contiguous.c > @@ -69,6 +69,19 @@ static int __init early_cma(char *p) > } > early_param("cma", early_cma); > > +#ifdef CONFIG_DMA_PERNUMA_CMA > + > +static struct cma *dma_contiguous_pernuma_area[MAX_NUMNODES]; > +static phys_addr_t pernuma_size_bytes __initdata; > + > +static int __init early_pernuma_cma(char *p) > +{ > + pernuma_size_bytes = memparse(p, &p); > + return 0; > +} > +early_param("pernuma_cma", early_pernuma_cma); > +#endif > + > #ifdef CONFIG_CMA_SIZE_PERCENTAGE > > static phys_addr_t __init __maybe_unused cma_early_percent_memory(void) > @@ -96,6 +109,34 @@ static inline __maybe_unused phys_addr_t cma_early_percent_memory(void) > > #endif > > +#ifdef CONFIG_DMA_PERNUMA_CMA > +void __init dma_pernuma_cma_reserve(void) > +{ > + int nid; > + > + if (!pernuma_size_bytes) > + return; > + > + for_each_online_node(nid) { > + int ret; > + char name[20]; > + struct cma **cma = &dma_contiguous_pernuma_area[nid]; > + > + snprintf(name, sizeof(name), "pernuma%d", nid); > + ret = cma_declare_contiguous_nid(0, pernuma_size_bytes, 0, 0, > + 0, false, name, cma, nid); > + if (ret) { > + pr_warn("%s: reservation failed: err %d, node %d", __func__, > + ret, nid); > + continue; > + } > + > + pr_debug("%s: reserved %llu MiB on node %d\n", __func__, > + (unsigned long long)pernuma_size_bytes / SZ_1M, nid); > + } > +} > +#endif > + > /** > * dma_contiguous_reserve() - reserve area(s) for contiguous memory handling > * @limit: End address of the reserved memory (optional, 0 for any). > @@ -228,23 +269,44 @@ static struct page *cma_alloc_aligned(struct cma *cma, size_t size, gfp_t gfp) > * @size: Requested allocation size. > * @gfp: Allocation flags. > * > - * This function allocates contiguous memory buffer for specified device. It > - * tries to use device specific contiguous memory area if available, or the > - * default global one. > + * tries to use device specific contiguous memory area if available, or it > + * tries to use per-numa cma, if the allocation fails, it will fallback to > + * try default global one. > * > - * Note that it byapss one-page size of allocations from the global area as > - * the addresses within one page are always contiguous, so there is no need > - * to waste CMA pages for that kind; it also helps reduce fragmentations. > + * Note that it bypass one-page size of allocations from the per-numa and > + * global area as the addresses within one page are always contiguous, so > + * there is no need to waste CMA pages for that kind; it also helps reduce > + * fragmentations. > */ > struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp) > { > +#ifdef CONFIG_DMA_PERNUMA_CMA > + int nid = dev_to_node(dev); > +#endif > + > /* CMA can be used only in the context which permits sleeping */ > if (!gfpflags_allow_blocking(gfp)) > return NULL; > if (dev->cma_area) > return cma_alloc_aligned(dev->cma_area, size, gfp); > - if (size <= PAGE_SIZE || !dma_contiguous_default_area) > + if (size <= PAGE_SIZE) > + return NULL; > + > +#ifdef CONFIG_DMA_PERNUMA_CMA > + if (nid != NUMA_NO_NODE && !(gfp & (GFP_DMA | GFP_DMA32))) { > + struct cma *cma = dma_contiguous_pernuma_area[nid];
It could be that for some node reservation failedm than dma_contiguous_pernuma_area[nid] would be NULL. I'd add a fallback to another node here.
> + struct page *page; > + > + if (cma) { > + page = cma_alloc_aligned(cma, size, gfp); > + if (page) > + return page; > + } > + } > +#endif
I think the selection of the area can be put in a helper funciton and then here we just try to allocate from the selected area. E.g.
static struct cma* dma_get_cma_area(struct device *dev) { #ifdef CONFIG_DMA_PERNUMA_CMA int nid = dev_to_node(dev); struct cma *cma = dma_contiguous_pernuma_area[nid];
if (!cma) /* select cma from another node */ ; return cma; #else return dma_contiguous_default_area; #endif }
struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp) { struct cma *cma; ...
cma = dma_get_cma_area(dev); if (!cma) return NULL;
return cma_alloc_aligned(cma, size, gfp); } > + if (!dma_contiguous_default_area) > return NULL; > + > return cma_alloc_aligned(dma_contiguous_default_area, size, gfp); > } > > @@ -261,9 +323,27 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp) > */ > void dma_free_contiguous(struct device *dev, struct page *page, size_t size) > { > - if (!cma_release(dev_get_cma_area(dev), page, > - PAGE_ALIGN(size) >> PAGE_SHIFT)) > - __free_pages(page, get_order(size));
Here as well, dev_get_cma_area() can be replaced with, say dma_get_dev_cma_area(dev, page) that will hide the below logic.
> + unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT; > + > + /* if dev has its own cma, free page from there */ > + if (dev->cma_area) { > + if (cma_release(dev->cma_area, page, count)) > + return; > + } else { > + /* > + * otherwise, page is from either per-numa cma or default cma > + */ > +#ifdef CONFIG_DMA_PERNUMA_CMA > + if (cma_release(dma_contiguous_pernuma_area[page_to_nid(page)], > + page, count)) > + return; > +#endif > + if (cma_release(dma_contiguous_default_area, page, count)) > + return; > + } > + > + /* not in any cma, free from buddy */ > + __free_pages(page, get_order(size)); > } > > /* > -- > 2.27.0 > >
-- Sincerely yours, Mike.
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