Path: ...!weretis.net!feeder9.news.weretis.net!panix!.POSTED.spitfire.i.gajendra.net!not-for-mail
From: cross@spitfire.i.gajendra.net (Dan Cross)
Newsgroups: comp.arch
Subject: Re: MSI interrupts
Date: Wed, 19 Mar 2025 14:03:56 -0000 (UTC)
Organization: PANIX Public Access Internet and UNIX, NYC
Message-ID: <vreisc$dqb$1@reader1.panix.com>
References: <vqto79$335c6$1@dont-email.me> <ohjCP.37185$SVG3.13173@fx42.iad> <vrcqcr$3ddah$1@dont-email.me> <36b8c18d145cdcd673713b7074cce6c3@www.novabbs.org>
Injection-Date: Wed, 19 Mar 2025 14:03:56 -0000 (UTC)
Injection-Info: reader1.panix.com; posting-host="spitfire.i.gajendra.net:166.84.136.80";
	logging-data="14155"; mail-complaints-to="abuse@panix.com"
X-Newsreader: trn 4.0-test77 (Sep 1, 2010)
Originator: cross@spitfire.i.gajendra.net (Dan Cross)
Bytes: 2169
Lines: 33

In article <36b8c18d145cdcd673713b7074cce6c3@www.novabbs.org>,
MitchAlsup1 <mitchalsup@aol.com> wrote:
>I want to address the elephant in the room::
>
>Why disable interrupts AT ALL !!

So that you can have some mechanism for building critical
sections that span multiple instructions, where just having
access to atomics and spin locks isn't enough.

>When running at any privilege, do you not want to accept an interrupt
>at higher priority with as little delay as possible ??

Usually the assumption is that the critical section is short; a
handful of instructions, perhaps, so that the cost of blocking a
high priority interrupt is low.

>Does Interrupt Disable help in this goal ??

This is predicated on an incomplete view of the situation and
the intersection between hardware and software.  Serving high
priority interrupts quickly is not the only consideration.

>Is there a SANE way to avoid disabling of interrupts ??

It depends on your definition of "sane" in this context.  One
may imagine redesigning all of a system's locking primitives,
perhaps, to avoid the need to block interrupts in most cases.
But that pushes a lot of complexity onto software for dubious
benefit, and even then, it's not clear to me that they can be
blocked in _all_ cases.

	- Dan C.