Messages in this thread | | | From | Zach Brown <> | Subject | Re: [PATCH 2 of 4] Introduce i386 fibril scheduling | Date | Thu, 1 Feb 2007 13:52:13 -0800 |
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> let me clarify this: i very much like your AIO patchset in general, in > the sense that it 'completes' the AIO implementation: finally > everything > can be done via it, greatly increasing its utility and hopefully its > penetration. This is the most important step, by far.
We violently agree on this :).
> what i dont really like /the particular/ concept above - the > introduction of 'fibrils' as a hard distinction of kernel threads. > They > are /almost/ kernel threads, but still by being different they create > alot of duplication and miss out on a good deal of features that > kernel > threads have naturally.
I might quibble with some of the details, but I understand your fundamental concern. I do. I don't get up each morning *thrilled* by the idea of having to update lockdep, sysrq-t, etc, to understand these fibril things :). The current fibril switch isn't nearly as clever as the lock-free task scheduling switch. It'd be nice if we didn't have to do that work to optimize the hell out of it, sure.
> It kind of hurts to say this because i'm usually quite concept-happy - > one can easily get addicted to the introduction of new core kernel > concepts :-)
:)
> so my suggestions center around the notion of extending kernel threads > to support the features you find important in fibrils: > >> would it be hard to redo your AIO patches based on a pool of plain >> simple kernel threads?
It'd certainly be doable to throw together a credible attempt to service "asys" system call submission with full-on kernel threads. That seems like reasonable due diligence to me. If full-on threads are almost as cheap, great. If fibrils are so much cheaper that they seem to warrant investing in, great.
I am concerned about the change in behaviour if we fall back to full kernel threads, though. I really, really, want aio syscalls to behave just like sync ones.
Would your strategy be to update the syscall implementations to share data in task_struct so that there isn't as significant a change in behaviour? (sharing current->ioprio, instead if just inheriting it, for example.). We'd be betting that there would be few of these and that they'd be pretty reasonable to share?
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