Re: Linux 2.6.17-rc2

[Jens Axboe <axboe@suse.de>]

On Thu, Apr 20 2006, Linh Dang wrote:
> Jens Axboe <axboe@suse.de> wrote:
> 
> > On Wed, Apr 19 2006, Linus Torvalds wrote:
> >> There are some other buffer management system calls that I haven't
> >> done yet (and when I say "I haven't done yet", I obviously mean
> >> "that I hope some other sucker will do for me, since I'm lazy"),
> >> but that are obvious future extensions:
> >
> > Well it's worked so far, hasn't it? :-)
> >
> >> - an ioctl/fcntl to set the maximum size of the buffer. Right now
> >>   it's
> >> hardcoded to 16 "buffer entries" (which in turn are normally limited to 
> >> one page each, although there's nothing that _requires_ that a buffer 
> >> entry always be a page).
> >
> > This is on a TODO, but not very high up since I've yet to see a case
> > where the current 16 page limitation is an issue. I'm sure something
> > will come up eventually, but until then I'd rather not bother.
> 
> DVD burning! splicing those huge VOB files into the dvd device would
> be nice. And believe me, the current 16 entries of the pipe is nowhere
> enough to sustain burning at 8X avg speed or higher.
> 
> It's a special case but it'd benefit a LOT of ppl ;-)

(don't drop the cc list)

DVD burning probably isn't a good splice fit, since you need to do more
than actually just point the device at the data. SG_IO is already
zero-copy as it maps the user data into the kernel without copying, so
there's very little room for improvement there to begin with.

-- 
Jens Axboe