Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: A peek at the future of storage | Date | Wed, 12 Dec 2007 10:02:44 -0800 |
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On Wednesday 12 December 2007 09:46, J. Bruce Fields wrote: > On Wed, Dec 12, 2007 at 08:46:18AM -0800, Daniel Phillips wrote: > > Incidentally, we ran our tests with 128 knfsd threads. The default > > of 8 threads produces miserable performance on the SSD, which gave > > us a good scare on our initial test run. It would be very nice to > > implement an algorithm to scale the knfsd thread pool > > automatically, in order to eliminate this class of thing that can > > go wrong. If somebody became inspired to take on that little > > project that would be great, otherwise it is in our pipeline for, > > hmm, Christmas delivery. (Exactly which Christmas is left > > unspecified.) > > People have proposed writing a daemon that just reads > /proc/net/rpc/nfsd periodically and uses that to adjust the number of > threads from userspace, probably subject to some limits in a config > file someplace. (Think that could do the job, or is there some reason > this would be easier in the kernel?)
I didn't actually say "kernel", though that was what I was thinking, perhaps just out of habit. It seems to me it would be a relatively small change to the existing code, essentially just finishing the idea, without needing to be patched up by userspace.
So how would a userspace daemon know that kernel is blocking and new threads are needed? In kernel this is pretty easy: when a new request arrives, look on the thread list and if none are available, generate a new one. Something special needs to be done to handle the case where there are no threads available because they are all piled up on a semaphore due to, for example, somebody unplugging the network cable for a remote disk. We have to avoid generating infinite threads in that case. Ideas?
Daniel
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