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 14:33:39 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>, 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
Subject: Re: [PATCH 2/2 v2] x86 idle: remove 32-bit-only "no-hlt" parameter, hlt_works_ok flag

Yes... safer that way.

Borislav Petkov <bp@...en8.de> wrote:

>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...

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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