On Wed, Jul 04, 2001 at 23:42:50 -0700, Mike Smith wrote:
> > On Wed, Jul 04, 2001 at 20:18:51 -0400, Kevin Hui wrote:
> > > Then the question is whether the kernel is copying data between userspace
> > > and kernelspace or whether it just DMAs the data straight in/out of the
> > > user program's address space. In Linux raw-io, given that it is a block
> > > device and you are doing page-aligned block I/Os on it, is smart and does
> > > zero copies. While it may seem to be jumping through hoops, maybe it does
> > > have a performance advantage?
> >
> > The kernel copies between userland and the kernel.
>
> Er, no.
>
> See sys/kern/kern_physio.c for the details.
*hits head*
I (of all people) should have remembered that. I wrote the zero copy stuff
for the pass(4) driver (see cam_periph_mapmem() in sys/cam/cam_periph.c)
using physio as a model.
Ken
--
Kenneth Merry
[EMAIL PROTECTED]
To Unsubscribe: send mail to [EMAIL PROTECTED]
with "unsubscribe freebsd-hackers" in the body of the message
