Re: Is sendfile all that sexy?

[Roman Zippel]

Hi,

On Thu, 18 Jan 2001, Linus Torvalds wrote:

> > Actually, this is a great example, because at one point I was working
> > on a device interface which would offload all of the disk-disk copying
> > overhead to the disks themselves, and not involve the CPU/RAM at all.
> 
> It's a horrible example.
> 
> device-to-device copies sound like the ultimate thing. 
> 
> They suck. They add a lot of complexity and do not work in general. And,
> if your "normal" usage pattern really is to just move the data without
> even looking at it, then you have to ask yourself whether you're doing
> something worthwhile in the first place.
> 
> Not going to happen.

device-to-device is not the same as disk-to-disk. A better example would
be a streaming file server. Slowly the pci bus becomes a bottleneck, why
would you want to move the data twice over the pci bus if once is enough
and the data very likely not needed afterwards? Sure you can use a more
expensive 64bit/60MHz bus, but why should you if the 32bit/30MHz bus is
theoretically fast enough for your application?
So I'm not advising it as "the ultimate thing", but I don't understand,
why it shouldn't happen.

bye, Roman