linux-kernel - Re: [PATCH 2/2 v2] x86 idle: remove 32-bit-only "no-hlt" parameter, hlt_works

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Date:	Sun, 10 Feb 2013 23:26:18 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Len Brown <lenb@...nel.org>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Len Brown <len.brown@...el.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/2 v2] x86 idle: remove 32-bit-only "no-hlt" parameter,
 hlt_works_ok flag

On Sun, Feb 10, 2013 at 04:37:27PM -0500, Len Brown wrote:
> From: Len Brown <len.brown@...el.com>
> 
> Remove 32-bit x86 a cmdline param "no-hlt",
> and the cpuinfo_x86.hlt_works_ok that it sets.
> 
> If a user wants to avoid HLT, then "idle=poll"
> is much more useful, as it avoids invocation of HLT
> in idle, while "no-hlt" failed to do so.
> 
> Indeed, hlt_works_ok was consulted in only 3 places.
> 
> First, in /proc/cpuinfo where "hlt_bug yes"
> would be printed if and only if the user booted
> the system with "no-hlt" -- as there was no other code
> to set that flag.
> 
> Second, check_hlt() would not invoke halt() if "no-hlt"
> were on the cmdline.
> 
> Third, it was consulted in stop_this_cpu(), which is invoked
> by native_machine_halt()/reboot_interrupt()/smp_stop_nmi_callback() --
> all cases where the machine is being shutdown/reset.
> The flag was not consulted in the more frequently invoked
> play_dead()/hlt_play_dead() used in processor offline and suspend.
> 
> Since Linux-3.0 there has been a run-time notice upon "no-hlt" invocations
> indicating that it would be removed in 2012.
> 
> Signed-off-by: Len Brown <len.brown@...el.com>
> Cc: x86@...nel.org
> ---
> v2: remove also check_hlt()

[ … ]

> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index 3286a92..e280253 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -28,7 +28,6 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
>  {
>  	seq_printf(m,
>  		   "fdiv_bug\t: %s\n"
> -		   "hlt_bug\t\t: %s\n"

Are we fine with changing /proc/cpuinfo output? We tend to consider it
an API to userspace, judging by past experience...

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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