How to best send files over network?

[Mikhail T.]

On 11.01.2012 13:29, Bob Friesenhahn wrote:
> Yes, I am definitely talking about the receive (or the writing end).

Well, this topic is of no concern to me right now -- I'm sending to clients 
already written (and embedded in firmwares), hence the explicit subject line :-)

> The main advantage of using sendfile() seems to be to keep the file data from 
> needing to transit a user-space program. This is a noble goal but 
> circumstances have changed (i.e. bottlenecks have moved) since sendfile() was 
> invented.

Even if other things involved in sending a file cost more, memory copying is 
still not free...

> If FreeBSD sendfile is using memory mapping in its implementation, then that 
> is definitely bad for zfs.

In September K. Macy claimed on this mailing list, that sending from mmap is 
over twice faster than sendfile, if the file is on ZFS:

    http://freebsd.1045724.n5.nabble.com/ZFS-lighttpd2-sendfile-too-high-IO-td4793886.html

Bob replied to that, actually, so he must remember the discussion :)

Though I find this sorry state of sendfile() rather disheartening, reading the 
above thread got me thinking about using a different method for different 
filesystems. But if mmap/write is never (i.e. for both UFS and ZFS) any worse 
than sendfile, then I can simply always use mmap in all cases. And this is, what 
I wanted to discuss -- I thought, in some cases, sendfile can arrange for data 
to go from the disk controller to the network card directly...

Yours,

    -mi