Messages in this thread | | | Date | Sun, 03 Feb 2008 20:14:45 -0800 | From | Arjan van de Ven <> | Subject | Re: [rfc] direct IO submission and completion scalability issues |
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David Chinner wrote: > Hi Nick, > > When Matthew was describing this work at an LCA presentation (not > sure whether you were at that presentation or not), Zach came up > with the idea that allowing the submitting application control the > CPU that the io completion processing was occurring would be a good > approach to try. That is, we submit a "completion cookie" with the > bio that indicates where we want completion to run, rather than > dictating that completion runs on the submission CPU. > > The reasoning is that only the higher level context really knows > what is optimal, and that changes from application to application.
well.. kinda. One of the really hard parts of the submit/completion stuff is that the slab/slob/slub/slib allocator ends up basically "cycling" memory through the system; there's a sink of free memory on all the submission cpus and a source of free memory on the completion cpu. I don't think applications are capable of working out what is best in this scenario..
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