Hello Shivank, On 02-04-21, 16:07, Shivank Garg wrote: > Hi Everyone, Always CC maintainers, scripts/get_maintainer.pl is your friend, use it > I'm a kernel newbie and M.Tech student at IIT Kanpur, India. I'm > researching DMA and DMAEngine for my thesis. I want to thank the > community for the dmatest.c program, It has helped me very much to get > an idea about using DMA api and writing a custom kernel module with > it. I'm stuck with the following doubts: > 1. How to find which DMAEngine controller my Linux system is using. I > read about I/OAT by intel and I guess this is the one my system is > using, But I can't get it from my hardware or Linux kernel. I also > want to know about my DMAEngine Controller specifications, like number > of channels, bandwidth, latency etc. /sys/class/dma/ would tell you the dmaengine channels available on a system > 2. Is DMA channel a software abstraction? How is it actually related > to DMA hardware? Are multiple DMA channels multiplexed to some single > entity. Also, if it's software abstraction, why can I only request a > maximum of 16 DMA channels on my machine? > Earlier I thought using multiple DMA channels would be like using a > multi-lane highway which would be very fast, but My experiments on > using multiple DMA channels simultaneously actually worsen the > performance (compared with single DMA channel) In theory things like dmaengine virtual channels are backed by hardware channels. Now most of the implementations use 1:1 mapping b/w virtual channels and hardware, it need not be so > 3. I read Efficient Asynchronous Memory Copy Operations on Multi-Core > Systems and I/OAT by K. Vaidyanathan, which helped me a lot. But still > some of my above questions remain uncleared. > > Also, a general doubt, to what extent the DMAEngine controller is > utilized? I mean I observed the DMA is used for high-speed network > packet copying in servers, and various applications ( like memory > devices, video devices) propose to use the DMAEngine, Do we have > enough DMA resources to fulfill everyone's needs? That depends on the system. Typically system designers would try to provide for intended usages on a system. Also TI has some fancy hardware implementation - UDMA, you should look at that also as part of your research (drivers/dma/ti/k3-udma.c) -- ~Vinod
