On 10/11/2011 11:50 AM, Gleb Natapov wrote:
On Tue, Oct 11, 2011 at 11:26:14AM +0200, Avi Kivity wrote: > rep/ins is exactly like dma+wait for this use case: provide an > address, get a memory image in return. There's no need to add > another interface, we should just optimize the existing one. > rep/ins cannot be optimized to be as efficient as dma and remain to be correct at the same time. There are various corner cases that simplified "fast" implementation will likely miss. Like DF flag settings, delaying interrupts for too much, doing ins/outs to/from iomem (this is may be not a big problem unless userspace finds a way to trigger it). There are ways that current implementation can be optimized still though.
These can all go through the slow path, except interrupts, which need to be checked after every access.
But loading MBs of data through fw_cfg interface is just abusing it. You wouldn't use pio on real HW to move megabytes of data and expect good performance.
True, this is a point in favour of a true dma interface. -- error compiling committee.c: too many arguments to function
