linux-kernel - Re: [PATCH v17 1/3] proc: add /proc/<pid>/arch

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Message-ID: <alpine.DEB.2.21.1904250917400.1762@nanos.tec.linutronix.de>
Date:   Thu, 25 Apr 2019 09:20:25 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Li, Aubrey" <aubrey.li@...ux.intel.com>
cc:     mingo@...hat.com, peterz@...radead.org, hpa@...or.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
        dave.hansen@...el.com, arjan@...ux.intel.com, adobriyan@...il.com,
        akpm@...ux-foundation.org, aubrey.li@...el.com,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v17 1/3] proc: add /proc/<pid>/arch_status

On Thu, 25 Apr 2019, Li, Aubrey wrote:

> On 2019/4/25 5:18, Thomas Gleixner wrote:
> > On Mon, 22 Apr 2019, Aubrey Li wrote:
> >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> >> index 5ad92419be19..d5a9c5ddd453 100644
> >> --- a/arch/x86/Kconfig
> >> +++ b/arch/x86/Kconfig
> >> @@ -208,6 +208,7 @@ config X86
> >>  	select USER_STACKTRACE_SUPPORT
> >>  	select VIRT_TO_BUS
> >>  	select X86_FEATURE_NAMES		if PROC_FS
> >> +	select PROC_PID_ARCH_STATUS		if PROC_FS
> > 
> > Can you please stop mixing arch and proc code? There is no point in
> > enabling this on x86 right away.
> > 
> >> +
> >> +config PROC_PID_ARCH_STATUS
> >> +	bool "Enable /proc/<pid>/arch_status file"
> > 
> > Why is this switchable? x86 selects it if PROC_FS is enabled and all other
> > architectures are absolutely not interested in this.
> 
> Above and this, I was trying to avoid an empty arch_file on other architectures.
> In previous proposal the entry only exists on the platform with AVX512.

What's the benefit of having a conditional enabled empty file for all other
architectures? Nothing AFAICT.
 
> >> +/*
> >> + * Add support for task architecture specific output in /proc/pid/arch_status.
> >> + * task_arch_status() must be defined in asm/processor.h
> >> + */
> >> +#ifdef CONFIG_PROC_PID_ARCH_STATUS
> >> +# ifndef task_arch_status
> >> +# define task_arch_status(m, task)
> >> +# endif
> > 
> > What exactly is the point of this macro mess? If an architecture selects
> > CONFIG_PROC_PID_ARCH_STATUS then it has to provide proc_task_arch_status()
> > and the prototype should be in include/linux/proc_fs.h.
> 
> I was trying to address Andy's last comments. If we have the prototype in 
> include/linux/proc_fs.h, we'll have a weak function definition in fs/proc/array.c,
> which bloats other architectures.
> 
> In that way proc_task_arch_status() should be defined in asm/processor.h,
> but proc_task_arch_status() has four parameters, I don't want unnecessary
> "struct pid_namespace *ns" and "struct pid *pid" leaked into arch headers,
> so I defined task_arch_status(m, task) to avoid that.

This #define mess is ugly and pointless. Let the arch select
CONFIG_PROC_PID_ARCH_STATUS and if it selects it it has to provide the
function. No waek function required at all.

Thanks,

	tglx