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@xxxxxxxxxxxxxxxxx > 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- RI Safir 2002 http://www.nylxs.com - Leadership Development in Free Software http://www2.mrbrklyn.com/resources - Unpublished Archive http://www.coinhangout.com - coins!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 _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
