Subject: Re: Bus mastering to user space
To: G. Scott Lloyd <>
From: Todd T. Fries <>
List: tech-kern
Date: 07/18/1997 16:46:20
On Jul 18, G. Scott Lloyd wrote
> Do the *BSD's support bus mastering DMA devices that transfer to/from user
> memory? I've been told that Linux does not and will not.
> The goal here is to reduce the copying of data to support 100-200
> MBytes/sec devices. What is the fastest throughput anyone has achieved?

If you are talking about dma, it is not possible to do this because
of the fact that userspace is virtualized memory, which is fragmented,
and cannot be guaranteed in 64k chunks, which is required in pc hardware.

However, if you are talking about sparc workstations, then I understand
some/all (not sure) are capable of doing dma transfers to the virtual
memory addresses (meaning possible to do it to userland).

What is implemented, I do not know, merely letting you know what is possible.
Todd Fries ..