NetBSD Problem Report #59682

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Date: Thu,  2 Oct 2025 12:46:00 +0000 (UTC)
From: campbell+netbsd@mumble.net
Reply-To: campbell+netbsd@mumble.net
To: gnats-bugs@NetBSD.org
Subject: qemu idles CPUs by spinning them at 100%
X-Send-Pr-Version: www-1.0

>Number:         59682
>Category:       port-sparc
>Synopsis:       qemu idles CPUs by spinning them at 100%
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    jdc
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Oct 02 12:50:00 +0000 2025
>Closed-Date:    Wed Sep 16 06:05:04 +0000 2026
>Last-Modified:  Wed Sep 16 06:05:04 +0000 2026
>Originator:     Taylor R Campbell
>Release:        9, 10
>Organization:
The SparcBSD Qemu Excitation
>Environment:
>Description:

	Before this change, qemu would only idle one CPU, not all CPUs,
	when the system is idle, and instead spin the other CPUs at
	100% capacity:

Module Name:    src
Committed By:   jdc
Date:           Sat May 31 15:14:40 UTC 2025

Modified Files:
        src/sys/arch/sparc/dev: apc.c

Log Message:
Set the idle bit for all the CPU's on a multi-processor system.  QEMU uses
this to idle all of the emulated CPU's, otherwise only one CPU is idled.


To generate a diff of this commit:
cvs rdiff -u -r1.2 -r1.3 src/sys/arch/sparc/dev/apc.c

https://mail-index.netbsd.org/source-changes/2025/05/31/msg157080.html


>How-To-Repeat:

	1. boot multiprocessor NetBSD/sparc under qemu
	2. do nothing
	3. watch top(1) in the host and see 100% CPU usage


>Fix:

	1. pull up the patch above
	2. consider nixing #ifdef MULTIPROCESSOR -- the iteration over
	   CPUs should compile away into the same thing


>Release-Note:

>Audit-Trail:

Responsible-Changed-From-To: port-sparc-maintainer->jdc
Responsible-Changed-By: riastradh@NetBSD.org
Responsible-Changed-When: Sun, 05 Oct 2025 18:54:08 +0000
Responsible-Changed-Why:
Can I trouble you to pull this up?


From: Martin Husemann <martin@duskware.de>
To: Julian Coleman <jdc@coris.org.uk>
Cc: pullup-10@netbsd.org
Subject: Re: [pullup-10 #1181] Sparc APC vs. QEMU
Date: Mon, 20 Oct 2025 16:06:51 +0200

Pulled up to netbsd-10, changes entry:

sys/arch/sparc/dev/apc.c                        1.3

        sparc: hack to inform QEMU about idle CPUs.

Thanks!


From: "Julian Coleman" <jdc@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59682 CVS commit: src/sys/arch/sparc/dev
Date: Tue, 15 Sep 2026 18:15:35 +0000

 Module Name:	src
 Committed By:	jdc
 Date:		Tue Sep 15 18:15:35 UTC 2026

 Modified Files:
 	src/sys/arch/sparc/dev: apc.c

 Log Message:
 Remove the #ifdef MULTIPROCESSOR and just use the CPU iterator.
 PR 59682


 To generate a diff of this commit:
 cvs rdiff -u -r1.3 -r1.4 src/sys/arch/sparc/dev/apc.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: open->closed
State-Changed-By: jdc@NetBSD.org
State-Changed-When: Wed, 16 Sep 2026 06:05:04 +0000
State-Changed-Why:
Pulled up to 10 [pullup-10 #1181] and #ifdef MULTIPROCESSOR removed.


>Unformatted:

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