Current APIs only support allocating CMA pages as either coherent or writecombine. This seems to miss support for cached pages completely. The following patch seems to be the first obvious solution. More generally though, what should be the strategy for remapping with other memory types? Add a new function call each time? Thanks, Laura
There are currently no dma allocation APIs that support cached buffers. For some use cases, caching provides a signficiant performance boost that beats write-combining regions. Add apis to allocate and map a cached DMA region. Signed-off-by: Laura Abbott <lauraa <at> codeaurora.org> --- arch/arm/include/asm/dma-mapping.h | 21 +++++++++++++++++++++ arch/arm/mm/dma-mapping.c | 21 +++++++++++++++++++++ 2 files changed, 42 insertions(+), 0 deletions(-) diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h index dc988ff..1565403 100644 --- a/arch/arm/include/asm/dma-mapping.h +++ b/arch/arm/include/asm/dma-mapping.h <at> <at> -239,12 +239,33 <at> <at> int dma_mmap_coherent(struct device *, struct vm_area_struct *, extern void *dma_alloc_writecombine(struct device *, size_t, dma_addr_t *, gfp_t); +/** + * dma_alloc_cached - allocate cached memory for DMA + * <at> dev: valid struct device pointer, or NULL for ISA and EISA-like devices + * <at> size: required memory size + * <at> handle: bus-specific DMA address + * + * Allocate some cached memory for a device for + * performing DMA. This function allocates pages, and will + * return the CPU-viewed address, and sets <at> handle to be the + * device-viewed address. + */(Continue reading)
On Fri, Jul 13, 2012 at 1:01 PM, Laura Abbott <lauraa <at> codeaurora.org> wrote: > There are currently no dma allocation APIs that support cached > buffers. For some use cases, caching provides a signficiant > performance boost that beats write-combining regions. Add > apis to allocate and map a cached DMA region. btw, there were recent patches for allocating dma memory without a virtual mapping. With this you could map however you want to userspace (for example, cached) I'm assuming that you are not needing it to be mapped cached to kernel? BR, -R > Signed-off-by: Laura Abbott <lauraa <at> codeaurora.org> > --- > arch/arm/include/asm/dma-mapping.h | 21 +++++++++++++++++++++ > arch/arm/mm/dma-mapping.c | 21 +++++++++++++++++++++ > 2 files changed, 42 insertions(+), 0 deletions(-) > > diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h > index dc988ff..1565403 100644 > --- a/arch/arm/include/asm/dma-mapping.h > +++ b/arch/arm/include/asm/dma-mapping.h > <at> <at> -239,12 +239,33 <at> <at> int dma_mmap_coherent(struct device *, struct vm_area_struct *, > extern void *dma_alloc_writecombine(struct device *, size_t, dma_addr_t *, > gfp_t); > > +/**(Continue reading)
On 7/14/2012 6:53 AM, Clark, Rob wrote: > On Fri, Jul 13, 2012 at 1:01 PM, Laura Abbott <lauraa <at> codeaurora.org> wrote: >> There are currently no dma allocation APIs that support cached >> buffers. For some use cases, caching provides a signficiant >> performance boost that beats write-combining regions. Add >> apis to allocate and map a cached DMA region. > > btw, there were recent patches for allocating dma memory without a > virtual mapping. With this you could map however you want to > userspace (for example, cached) > > I'm assuming that you are not needing it to be mapped cached to kernel? > Thanks for reminding me about those patches. They don't quite solve the problem as is for two reasons: 1) I'm looking at regular CMA allocations, not iommu allocations which is what the patches covered 2) I do actually need a kernel cached mapping in addition to the userspace mappings. I've obviously missed the last DMA rework patches, and I should rebase/rework against those. Is another DMA attribute (DMA_ATTR_CACHED) an acceptable option? > BR, > -R > Thanks, Laura(Continue reading)
Hi Laura, On Friday, July 13, 2012 8:02 PM Laura Abbott wrote: > There are currently no dma allocation APIs that support cached > buffers. For some use cases, caching provides a signficiant > performance boost that beats write-combining regions. Add > apis to allocate and map a cached DMA region. > > Signed-off-by: Laura Abbott <lauraa <at> codeaurora.org> I agree that there is a need for cached contiguous memory blocks. I see that your patch is based on some older version of CMA/dma-mapping code. In v3.5-rc1 CMA has been merged to mainline kernel together with DMA-mapping redesign patches, so an attribute approach can be used instead of adding new functions to the API. My original idea was to utilize the dma_alloc_nonconsistent() call and DMA_ATTR_NONCONSISTENT for allocating/mapping cached contiguous buffers, but I didn't have enough time for completing this work. The main missing piece is the API for managing cache synchronization on such buffers. There is a dma_cache_synch() functions but it is broken from the API point of view. To replace it with something better, some additional work is needed for all drivers which already use it. Also some work in needed for cleanup dma_alloc_nonconsistent() implementations for all the architectures using dma_map_ops approach. All this is on my TODO list, but I currently I'm really busy with other tasks related to CMA (mainly bugfixes for some special use-cases). > --- > arch/arm/include/asm/dma-mapping.h | 21 +++++++++++++++++++++ > arch/arm/mm/dma-mapping.c | 21 +++++++++++++++++++++ > 2 files changed, 42 insertions(+), 0 deletions(-)(Continue reading)
On 7/16/2012 10:58 PM, Marek Szyprowski wrote: > Hi Laura, > > On Friday, July 13, 2012 8:02 PM Laura Abbott wrote: > >> There are currently no dma allocation APIs that support cached >> buffers. For some use cases, caching provides a signficiant >> performance boost that beats write-combining regions. Add >> apis to allocate and map a cached DMA region. >> >> Signed-off-by: Laura Abbott <lauraa <at> codeaurora.org> > > I agree that there is a need for cached contiguous memory blocks. I see that your patch > is based on some older version of CMA/dma-mapping code. In v3.5-rc1 CMA has been merged > to mainline kernel together with DMA-mapping redesign patches, so an attribute approach > can be used instead of adding new functions to the API. My original idea was to utilize > the dma_alloc_nonconsistent() call and DMA_ATTR_NONCONSISTENT for allocating/mapping > cached contiguous buffers, but I didn't have enough time for completing this work. > > The main missing piece is the API for managing cache synchronization on such buffers. > There is a dma_cache_synch() functions but it is broken from the API point of view. To > replace it with something better, some additional work is needed for all drivers which > already use it. Also some work in needed for cleanup dma_alloc_nonconsistent() > implementations for all the architectures using dma_map_ops approach. All this is on my > TODO list, but I currently I'm really busy with other tasks related to CMA (mainly > bugfixes for some special use-cases). > In what is the dma_cache_sync API broken? Just curious at this point.(Continue reading)
> -----Original Message----- > From: Laura Abbott [mailto:lauraa <at> codeaurora.org] > Sent: Friday, July 20, 2012 10:30 PM > To: Marek Szyprowski > Cc: linaro-mm-sig <at> lists.linaro.org; 'Russell King'; linux-arm-msm <at> vger.kernel.org; linux-(Continue reading)arm- > kernel <at> lists.infradead.org > Subject: Re: [PATCH][RFC] arm: dma-mapping: Add support for allocating/mapping cached buffers > > On 7/16/2012 10:58 PM, Marek Szyprowski wrote: > > Hi Laura, > > > > On Friday, July 13, 2012 8:02 PM Laura Abbott wrote: > > > >> There are currently no dma allocation APIs that support cached > >> buffers. For some use cases, caching provides a signficiant > >> performance boost that beats write-combining regions. Add > >> apis to allocate and map a cached DMA region. > >> > >> Signed-off-by: Laura Abbott <lauraa <at> codeaurora.org> > > > > I agree that there is a need for cached contiguous memory blocks. I see that your patch > > is based on some older version of CMA/dma-mapping code. In v3.5-rc1 CMA has been merged > > to mainline kernel together with DMA-mapping redesign patches, so an attribute approach > > can be used instead of adding new functions to the API. My original idea was to utilize > > the dma_alloc_nonconsistent() call and DMA_ATTR_NONCONSISTENT for allocating/mapping > > cached contiguous buffers, but I didn't have enough time for completing this work. > > > > The main missing piece is the API for managing cache synchronization on such buffers. > > There is a dma_cache_synch() functions but it is broken from the API point of view. To
On Monday 23 July 2012, Marek Szyprowski wrote: > I would like to completely remove dma_cache_sync() and replace it with > dma_sync_single_for_cpu/device(), but this probably require a bit more > discussion and fixing all current clients of dma_cache_sync(). Sounds like a good idea. Fortunately, there are only a handful of such drivers in the kernel, and even fewer machines that actually need this, so we should be able to find all the people that care about these. Arnd
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