Q: dma requires copying into dma buffer - so what's the benefit ?
Hello, There is something I don't understand about dma, when doing memory to memory dma, it requires to cllocate dma buffer (for example with dma_alloc_coherent), than for each transfer we need to copy the buffer to the allocated memory and than trigger dma transaction. So, if it requires additional memcpy for each transaction , what's the benefit of using dma ? without dma: 1. copy buffer (memcpy) from source to destination with dma: 1. copy buffer (memcpy) from source to dma buffer 2. trigger dma transaction (which shall copy the buffer eventually to destination buffer) Regards, Ran
On 09/06/2016 12:24 PM, Ran Shalit wrote:
Hello,
There is something I don't understand about dma, when doing memory to memory dma, it requires to cllocate dma buffer (for example with dma_alloc_coherent), than for each transfer we need to copy the buffer to the allocated memory and than trigger dma transaction. So, if it requires additional memcpy for each transaction , what's the benefit of using dma ?
without dma: 1. copy buffer (memcpy) from source to destination
with dma: 1. copy buffer (memcpy) from source to dma buffer 2. trigger dma transaction (which shall copy the buffer eventually to destination buffer)
DMA hardware uses an expedited bus that frees the main memory to be addressed for other processes.
Regards, Ran
_______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
-- So many immigrant groups have swept through our town that Brooklyn, like Atlantis, reaches mythological proportions in the mind of the world - RI Safir 1998 http://www.mrbrklyn.com DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002 http://www.nylxs.com - Leadership Development in Free Software http://www2.mrbrklyn.com/resources - Unpublished Archive http://www.coinhangout.com - coins! http://www.brooklyn-living.com Being so tracked is for FARM ANIMALS and and extermination camps, but incompatible with living as a free human being. -RI Safir 2013
participants (2)
-
Ran Shalit -
Ruben Safir