Messages in this thread | | | Date | Wed, 6 Nov 2002 02:05:05 -0500 | From | Benjamin LaHaise <> | Subject | Re: [PATCH 2/2] 2.5.46 AIO support for raw/O_DIRECT |
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On Tue, Nov 05, 2002 at 05:17:32PM -0800, Andrew Morton wrote: > Or not proceed with this patch at all. If this is to be the > only code which wishes to perform page list motion at interrupt > time, perhaps it's not justifiable? > > I really don't have a feeling for how valuable this is, nor > do I know whether there will be other code which wants to > perform page list manipulation at interrupt time.
I can think of a few other places that would like to perform page motion from irq context: anything else doing zero copy or page flipping, and more importantly the O(1) vm code that's being worked on. The latter is actually quite important as we've got a number of customers running into problems with some of the algorithms in the 2.4 kernel where the kernel does not perform any list motion from irq context and this results in excess cpu time spent traversing lists to see if io has completed.
> In fact I also don't know where the whole AIO thing sits at > present. Is it all done and finished? Is there more to come, > and if so, what??
There's more to come. The bits I'm working on are running in kernel context mainly to simplify the copy_*_user case since we don't have full zero copy semantics available and coping with pinned pages is a challenge in a multiuser system, plus it makes reusing the existing networking code a lot easier. Basically, anything that involves a copy of data is likely to be better implemented running in a task to get the priority of execution correct, whereas anything involving zero copy io is going to want completion from irq or bottom half context and hence dirty pages. Does that make sense?
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