Hi,
I agree that it is not feasible to add new system calls every time
somebody has a problem, and we don't take adding system calls lightly.
However, in this case we're talking about an entire *community* of
people (high-end computing), not just one or two people. Of course it
may still be the case that that community is not important enough to
justify the addition of system calls; that's obviously not my call to make!
I'm sure that you meant more than just to rename openg() to lookup(),
but I don't understand what you are proposing. We still need a second
call to take the results of the lookup (by whatever name) and convert
that into a file descriptor. That's all the openfh() (previously named
sutoc()) is for.
I think the subject line might be a little misleading; we're not just
talking about NFS here. There are a number of different file systems
that might benefit from these enhancements (e.g. GPFS, Lustre, PVFS,
PanFS, etc.).
Finally, your comment on making filesystem developers miserable is sort
of a point of philosophical debate for me. I personally find myself
miserable trying to extract performance given the very small amount of
information passing through the existing POSIX calls. The additional
information passing through these new calls will make it much easier to
obtain performance without correctly guessing what the user might
actually be up to. While they do mean more work in the short term, they
should also mean a more straight-forward path to performance for
cluster/parallel file systems.
Thanks for the input. Does this help explain why we don't think we can
just work under the existing calls?
Rob
Latchesar Ionkov wrote:
Hi,
One general remark: I don't think it is feasible to add new system
calls every time somebody has a problem. Usually there are (may be not
that good) solutions that don't require big changes and work well
enough. "Let's change the interface and make the life of many
filesystem developers miserable, because they have to worry about
3-4-5 more operations" is not the easiest solution in the long run.
On 12/1/06, Rob Ross <[EMAIL PROTECTED]> wrote:
Hi all,
The use model for openg() and openfh() (renamed sutoc()) is n processes
spread across a large cluster simultaneously opening a file. The
challenge is to avoid to the greatest extent possible incurring O(n) FS
interactions. To do that we need to allow actions of one process to be
reused by other processes on other OS instances.
The openg() call allows one process to perform name resolution, which is
often the most expensive part of this use model. Because permission
If the name resolution is the most expensive part, why not implement
just the name lookup part and call it "lookup" instead of "openg". Or
even better, make NFS to resolve multiple names with a single request.
If the NFS server caches the last few name lookups, the responses from
the other nodes will be fast, and you will get your file descriptor
with two instead of the proposed one request. The performance could be
just good enough without introducing any new functions and file
handles.
Thanks,
Lucho
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