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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: MSI interrupts
Date: Mon, 24 Mar 2025 17:47:48 +0000
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On Mon, 24 Mar 2025 13:59:49 +0000, Scott Lurndal wrote:

> cross@spitfire.i.gajendra.net (Dan Cross) writes:
>>In article <4603ec2d5082f16ab0588b4b9d6f96c7@www.novabbs.org>,
>>MitchAlsup1 <mitchalsup@aol.com> wrote:
>
>>
>>>My architecture has a mechanism to perform ATOMIC stuff over multiple
>>>instruction time frames that has the property that a higher priority
>>>thread which interferers with a lower priority thread, the HPT wins
>>>and the LPT fails its ATOMIC event. It is for exactly this reason
>>>that I drag priority through the memory hierarchy--so that real-time
>>>things remain closer to real-time (no or limited priority inversions).
>>
>>Without being able to see this in practice, it's difficult to
>>speculate as to how well it will actually work in real-world
>>scenarios.  What is the scope of what's covered by this atomic
>>thing?
>
> Sounds a lot like transactional memory.  Something that has
> yet to prove to be usable in the general case.

It is not TM, but can be used to implement TM should you like.
It is a set of instructions that can implement any (known)
ATOMIC process (TestAndSet, TestAndTestAndSet; lock, unlock,
LD-locked, ST-conditional, CompareSwap, CompareDouble, SwapDouble
CompareTriple, SwapTriple, RemoveElement, InsertElement,
MoveElement, ...}

It is basically a recipe book so SW can implement whatever kinds
of ATOMIC things SW wants, leaving HW out of the loop.

you can also consider it a fully pipelined version of LDL and STC
with up to 8 cache lines of data available for the event.

>>
>>Consider something as simple as popping an item off of the front
>>of a queue and inserting it into an ordered singly-linked list:
>>In this case, I'm probably going to want to take a lock on the
>>queue, then lock the list, then pop the first element off of the
>>queue by taking a pointer to the head.
>
> Which can be done with compare and exchange, atomically;
> a lock may not be necessary.
>
> The insert into an ordered list will likely require a
> spin lock (or a reader-writer lock of some form).