userland access to devices is moving!

[Julian Elischer]

cool..
how does 'mount' do this however, as it doesn't have a fd list to wok
with. Or are you still leaving the vnode access path in place?


On Wed, 18 Jun 2003, Poul-Henning Kamp wrote:

> 
> I sat down and hacked up a simple prototype to test the concept I
> have been rambling about for some years:  Going directly from
> filedescriptor to device driver thus bypassing the vnode, devfs and
> specfs layer.
> 
> I implemented this for /dev/null and /dev/zero, and ran the simple
> benchmark "dd if=/dev/zero of=/dev/null count=1000000"
> 
> Before:
> N      3 Average:       44.900752667 Stddev:            0.049906338
> 
> After:
> N      3 Average:       18.460190333 Stddev:            0.074019507
> 
> That is 26.4 microseconds saved for each read(2)+write(2) operation,
> or 41% improvement on my Athlon 700MHz machine.
> 
> A bit more locking will probably be needed, so this will erode some
> of this number, but there will be something left I'm sure :-)
> 
> The largest impact of this is that VOP_OPEN(), vn_open() and
> vn_open_cred() grows an argument (the fdesc index) which existing
> callers need to pass a -1, the rest is relatively local hacking in
> devfs and some adjustments in the descriptor code.
> 
> I have overall found that the implementation of this is not as hard
> as I imagined, and if I doubted it before, I am now certain that
> this is the right way to go.
> 
> I should have tried this long time ago...
> 
> patch at:
> 	http://phk.freebsd.dk/patch/fdesc.patch
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
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