Subject: Re: Interrupt, interrupt threads, continuations, and kernel lwps
To: <>
From: haad <>
List: tech-kern
Date: 02/22/2007 00:59:23
Hash: SHA1

Bill Studenmund wrote:
> On Wed, Feb 21, 2007 at 10:51:03PM +0000, Andrew Doran wrote:
>> Hi Jason,
>> On Wed, Feb 21, 2007 at 10:01:44AM -0800, Jason Thorpe wrote:
>>> 2- Speed.  Because the low-level interrupt dispatch code could be  
>>> simple and avoid magic, it could be very fast, which would help  
>>> devices that are particularly sensitive to interrupt latency.
>> If you have a device that's particularly sensitive to interrupt latency,
>> then the two level model is a good one, I agree completely. There is
>> nothing to prevent that model from being used where it's a good fit.
>> For the general case, I don't agree though. On recent processors with long
>> instruction pipelines, serializing control operations are really expensive.
>> x86 chips from 5 years ago are faster in this regard than the current Intel
>> offerings - in real time, not clock cycles. I'm keen to avoid that kind of
>> "funneling" of work unless it's really neccessary - meaning, it's existence
>> actually has a justifiable benefit, So I have been trying to eliminate these
>> kinds of operations where they are unnecessary, e.g: during lock release,
>> during splx(), during syscalls, in the locking scheme devised for the
>> scheduler and so on.
>> What I want to do will on x86 add 29 arithmetic instructions to the
>> interrupt path (as of now). That's means in the common, non blocking case,
>> it's ~free. I'd be pretty bummed if we undo some of that and the reasoning
>> for doing so is to make the system a better fit for ~20 year old systems.
> Ok, that sounds good. How do we make this work on SPARC, m68k, and VAX? 
> Right now, interrupts-as-threads sounds like a total loss for them. If we 
> can turn it into something that's "about as good" then I think you will 
> just get a green light. :-)
> Take care,
> Bill
AFAIK solaris use the kernel threads for interrupts we can look at the open
solaris sources how the solved this issue with SPARC CPU architecture.

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