Re: Calculating kernel logical address ..

Daniel Phillips
2002-09-09T19:04:00Z

On Monday 09 September 2002 20:43, Richard B. Johnson wrote:
> On Mon, 9 Sep 2002, Daniel Phillips wrote:
>
> > On Monday 09 September 2002 20:00, Richard B. Johnson wrote:
> > > For some reason, (claimed performance reasons) user-mode code
> > > has to be able to get data directly from hardware with no
> > > intervening copy operation. I think any claimed advantage goes
> > > away when you look at the overhead necessary for user-mode
> > > code to sleep before, and awaken after, the DMA operation but
> > > often marketing departments make those decisions.
> >
> > Pfft. Try turning off ide dma and see what happens.
>
> I know that DMA works, I'm talking about DMA direct-to-user
> which is not what the file-systems that use DMA do.

The next generation of fast, parallel filesystems relies on dma
to/from user space. Besides, what do you think happens when you
read/write a mmap?

--
Daniel