Dave C Boutcher wrote:
On Thu, Dec 08, 2005 at 02:09:32PM -0600, Mike Christie wrote:
James Bottomley wrote:
On Thu, 2005-12-08 at 13:10 -0600, Mike Christie wrote:
cleanup. In the end some of the scsi people liked the idea of throwing
the non-read/write command to userspace and to do this we just decided
to start over but I have been cutting and pasting your code and cleaning
it up as I add more stuff.
To be honest, I'd like to see all command processing at user level
(including read/write ... for block devices, it shouldn't be that
inefficient, since you're merely going to say remap an area from one
device to another; as long as no data transformation ever occurs, the
user never touches the data and it all remains in the kernel page
cache).
Ok, Tomo and I briefly talked about this when we saw Jeff's post about
doing block layer drivers in userspace on lkml. I think we were somewhat
prepared for this given some of your other replies.
So Vlad and other target guys what do you think? Vlad are you going to
continue to maintain scst as kernel only, or is there some place we can
work together on this on - if your feelings are not hurt too much that
is :) ?
Oofff....Architecturally I agree with James...do all command processing
in one place. On the other hand, the processing involved with a read or
write in the normal case (no aborts/resets/ordering/timeouts/etc) is
almost zero. Figure out the LBA and length and pass on the I/O. The
overhead of passing it up and down across the kernel boundary is likely
to be orders of magnitude larger than the actual processing. I would
personally rather not fix this decision in concrete until we could do
some actual measurements of a SCSI target under heavy load.
Totally agree.
Vlad
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