On Thu, 16 Oct 2014, Chen, Xiaoxi wrote: > >Hi, indeed qemu use a single thread per queue. > >I think it's not a problem with common storage (nfs,scsi,..) because they > >use less cpu ressource than librbd, so you can reach > >easily > 100000iops with 1thread. > > I think it's a common problem shared by all storage backend(nfs,scsi), > but Ceph take longer time to sent out an IO(30us), while NFS and scsi is > really simple(no crush, no stripping, etc) that may only take 3us to > send out an IO, so the upper bound is 10X than ceph.
I would be very interested in seeing where the CPU time is actually spent. I know there are is some locking contention in librbd, but with the librados changes that layer at least should have have a much lower overhead. We also should be preserving mappings for PGs in most cases to avoid much time spent in CRUSH. It would be very interesting to be proven wrong, though! sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
