From: Ingo Molnar <mingo@elte.hu>
To: Len Brown <lenb@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
linux-pm@lists.linux-foundation.org,
Len Brown <len.brown@intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works_ok flag
Date: Thu, 31 Mar 2011 10:18:00 +0200 [thread overview]
Message-ID: <20110331081800.GH5938@elte.hu> (raw)
In-Reply-To: <alpine.LFD.2.02.1103310252160.8569@x980>
* Len Brown <lenb@kernel.org> wrote:
> > > 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.
Do we know whether a distro adds this to the boot line? Do we know about users
relying on it.
> "idle=poll" does the same thing -- sans change a line
> in /proc/cpuinfo.
It also has an effect on halt/poweroff, right?
> Do we really need both?
Probably not, as i said i do not disagree - i just think it should be more
explicit. Make it a: "users of CPU models X beware" commit title, not 'remove
inactive code' ...
So please list the affected hardware and list the affected boot parameter
explicitly, in a well-titled commit that phases out this (very likely unused)
compatibility hack and *document* the idle=poll workaround for ancient
hardware.
There's still i386DX CPUs being manufactured these days - a 20+ years old CPU
design is surprisingly resilient to spurious patent claims, for obvious
reasons.
Really, there's no need to do things by stealth. There's few things worse than
doing the right thing for the wrong reason - it becomes a bad habit of subtly
broken thinking quickly.
Thanks,
Ingo
next prev parent reply other threads:[~2011-03-31 8:18 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-24 7:08 [PATCH 0/5] x86 idle cruft removal Len Brown
2011-03-24 7:08 ` [PATCH 1/5] x86 idle: remove "no-hlt" cmdline param Len Brown
2011-03-24 7:08 ` [PATCH 2/5] x86 idle: remove NOP cpuinfo_x86.hlt_works_ok flag Len Brown
2011-03-24 7:08 ` [PATCH 3/5] x86 idle: remove NOP halt_works() Len Brown
2011-03-24 7:08 ` [PATCH 4/5] x86 idle floppy: delete disable_hlt()/enable_hlt() Len Brown
2011-03-24 15:58 ` Andi Kleen
2011-03-24 7:08 ` [PATCH 5/5] x86 idle: remove NOP hlt_use_halt() Len Brown
2011-03-25 19:02 ` [linux-pm] " Vaidyanathan Srinivasan
2011-03-31 6:03 ` [PATCH 0/9] x86 idle cruft removal - v2 Len Brown
2011-03-31 6:03 ` [PATCH 1/9] x86 idle: remove "no-hlt" cmdline param Len Brown
2011-03-31 6:03 ` [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works_ok flag Len Brown
2011-03-31 6:12 ` Ingo Molnar
2011-03-31 7:02 ` Len Brown
2011-03-31 8:18 ` Ingo Molnar [this message]
2011-03-31 9:23 ` Alan Cox
2011-03-31 9:27 ` Ingo Molnar
2011-03-31 9:33 ` Alan Cox
2011-03-31 9:35 ` Ingo Molnar
2011-03-31 14:19 ` H. Peter Anvin
2011-03-31 14:41 ` Alan Cox
2011-03-31 15:09 ` H. Peter Anvin
2011-03-31 18:07 ` Len Brown
2011-03-31 18:28 ` H. Peter Anvin
2011-03-31 6:03 ` [PATCH 3/9] x86 idle: remove NOP halt_works() Len Brown
2011-03-31 6:03 ` [PATCH 4/9] x86 idle floppy: delete disable_hlt()/enable_hlt() Len Brown
2011-03-31 6:03 ` [PATCH 5/9] x86 idle: remove NOP hlt_use_halt() Len Brown
2011-03-31 6:03 ` [PATCH 6/9] x86 idle APM: delete apm_cpu_idle(), and its use of (pm_idle)() Len Brown
2011-03-31 6:03 ` [PATCH 7/9] x86 idle: do not EXPORT_SYMBOL pm_idle and default_idle Len Brown
2011-03-31 6:03 ` [PATCH 8/9] x86 idle: move mwait_idle_with_hints() to where it is used Len Brown
2011-03-31 6:03 ` [PATCH 9/9] x86 idle: delete mwait_idle() Len Brown
2011-04-01 11:02 ` Andreas Herrmann
2011-03-31 6:39 ` [linux-pm] [PATCH 0/9] x86 idle cruft removal - v2 Trinabh Gupta
2011-03-31 7:21 ` Len Brown
2011-03-31 9:45 ` Alan Cox
2011-03-31 10:28 ` Ingo Molnar
2011-04-01 4:24 ` Len Brown
2011-04-01 9:38 ` [linux-pm] " Trinabh Gupta
2011-04-01 18:33 ` Len Brown
2011-04-02 6:22 ` idle cleanup - v3 Len Brown
2011-04-02 6:22 ` [PATCH 01/18] cpuidle: menu: fixed wrapping timers at 4.294 seconds Len Brown
2011-04-02 6:22 ` [PATCH 02/18] x86 idle floppy: deprecate disable_hlt() Len Brown
2011-04-02 6:22 ` [PATCH 03/18] x86 idle APM: deprecate CONFIG_APM_CPU_IDLE Len Brown
2011-04-02 11:28 ` Alan Cox
2011-04-02 18:28 ` Len Brown
2011-04-02 19:44 ` Alan Cox
2011-04-08 6:22 ` Pavel Machek
2011-04-02 6:22 ` [PATCH 04/18] x86 idle: EXPORT_SYMBOL(default_idle, pm_idle) only when APM demands it Len Brown
2011-04-02 11:28 ` Alan Cox
2011-04-02 12:21 ` [linux-pm] " Trinabh Gupta
2011-04-02 6:22 ` [PATCH 05/18] x86 idle: deprecate "no-hlt" cmdline param Len Brown
2011-04-02 6:22 ` [PATCH 06/18] x86 idle: deprecate mwait_idle() and "idle=mwait" " Len Brown
2011-04-02 6:22 ` [PATCH 07/18] x86 idle: clarify AMD erratum 400 workaround Len Brown
2011-04-02 8:23 ` Borislav Petkov
2011-04-02 19:19 ` Len Brown
2011-04-02 19:22 ` [PATCH 07/18] x86 idle: clarify AMD erratum 400 workaround -v2 Len Brown
2011-04-03 9:00 ` Borislav Petkov
2011-04-02 6:22 ` [PATCH 08/18] cpuidle: create bootparam "cpuidle.off=1" Len Brown
2011-07-15 11:27 ` [linux-pm] " Deepthi Dharwar
2011-04-02 6:22 ` [PATCH 09/18] cpuidle: replace xen access to x86 pm_idle and default_idle Len Brown
2011-04-04 15:33 ` [Xen-devel] " Konrad Rzeszutek Wilk
2011-04-02 6:22 ` [PATCH 10/18] x86 idle: move mwait_idle_with_hints() to where it is used Len Brown
2011-04-02 6:22 ` [PATCH 11/18] cpuidle: stop using pm_idle Len Brown
2011-04-25 10:41 ` [linux-pm] " Trinabh Gupta
2011-04-02 6:22 ` [PATCH 12/18] 2.6.40: x86 idle: remove deprecated "no-hlt" cmdline param Len Brown
2011-04-02 6:22 ` [PATCH 13/18] 2.6.40: x86 idle: remove deprecated "hlt_bug: no" in 32-bit /proc/cpuinfo Len Brown
2011-04-02 6:22 ` [PATCH 14/18] 2.6.40: x86 idle floppy: remove deprecated disable_hlt()/enable_hlt() Len Brown
2011-04-02 6:22 ` [PATCH 15/18] 2.6.40: x86 idle: remove deprecated hlt_use_halt() Len Brown
2011-04-02 6:22 ` [PATCH 16/18] 2.6.40: x86 idle APM: remove deprecated apm_cpu_idle() Len Brown
2011-04-02 11:40 ` Alan Cox
2011-04-02 19:44 ` Len Brown
2011-04-02 21:00 ` Alan Cox
2011-04-03 2:48 ` [linux-pm] " Trinabh Gupta
2011-04-04 10:05 ` Alan Cox
2011-04-02 6:22 ` [PATCH 17/18] 2.6.40: x86 idle: do not export default_idle() and (pm_idle)() Len Brown
2011-04-02 6:23 ` [PATCH 18/18] 2.6.40: x86 idle: remove deprecated mwait_idle() Len Brown
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