linux-kernel - Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works

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Message-id: <alpine.LFD.2.02.1103310252160.8569@x980>
Date:	Thu, 31 Mar 2011 03:02:00 -0400 (EDT)
From:	Len Brown <lenb@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org,
	Len Brown <len.brown@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works_ok flag

> > hlt_works_ok was X86_32 only, initialized to 1, and never cleared.
> > 
> > On 32-bit kernels, this deletes a line from /proc/cpuinfo: "hlt_bug : no"
> 
> I think you missed the valid usecase where an old CPU with broken halt is 
> booted with the no-hlt boot parameter and does not want to crash in the HLT 
> instruction.
> 
> That "no-hlt" boot parameter does:
> 
>   arch/x86/kernel/cpu/bugs.c:     boot_cpu_data.hlt_works_ok = 0;
> 
> We can restrict compatibility, but *please* lets do it *explicitly*, not under 
> some 'remove unused code' pretense ...
> 
> Could you please list all CPU models that are affected?

"no-hlt" existed only for 32-bit, and there were exactly zero
automatic invocations of it.

"idle=poll" does the same thing -- sans change a line
in /proc/cpuinfo.

Do we really need both?

thanks,
-Len



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