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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