linux-kernel - Re: [PATCH] arm64: restore bogomips information in /proc/cpuinfo

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Message-ID: <20151118184736.GM1588@arm.com>
Date:	Wed, 18 Nov 2015 18:47:36 +0000
From:	Will Deacon <will.deacon@....com>
To:	Yang Shi <yang.shi@...aro.org>
Cc:	Catalin.Marinas@....com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH] arm64: restore bogomips information in /proc/cpuinfo

Hello,

On Wed, Nov 18, 2015 at 10:15:05AM -0800, Yang Shi wrote:
> As what Pavel Machek reported [1], some userspace applications depend on
> bogomips showed by /proc/cpuinfo.
> 
> Although there is much less legacy impact on aarch64 than arm, but it does
> break libvirt.
> 
> Basically, this patch reverts commit 326b16db9f69fd0d279be873c6c00f88c0a4aad5
> ("arm64: delay: don't bother reporting bogomips in /proc/cpuinfo"), but with
> some tweak due to context change.
> 
> [1] https://lkml.org/lkml/2015/1/4/132

I lost this argument last time around, so I won't re-tread that path this
time around. I do, however, have some comments on the patch.

> 
> Signed-off-by: Yang Shi <yang.shi@...aro.org>
> ---
>  arch/arm64/kernel/cpuinfo.c | 5 +++++
>  arch/arm64/kernel/smp.c     | 7 ++++++-
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> index 706679d..8d4ba77 100644
> --- a/arch/arm64/kernel/cpuinfo.c
> +++ b/arch/arm64/kernel/cpuinfo.c
> @@ -30,6 +30,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/sched.h>
>  #include <linux/smp.h>
> +#include <linux/delay.h>
>  
>  /*
>   * In case the boot CPU is hotpluggable, we record its initial state and
> @@ -112,6 +113,10 @@ static int c_show(struct seq_file *m, void *v)
>  		 */
>  		seq_printf(m, "processor\t: %d\n", i);
>  
> +		seq_printf(m, "BogoMIPS\t: %lu.%02lu\n\n",

This double newline makes /proc/cpuinfo looks really odd. Can we just
have one, please?

> +			   loops_per_jiffy / (500000UL/HZ),
> +			   loops_per_jiffy / (5000UL/HZ) % 100);
> +
>  		/*
>  		 * Dump out the common processor features in a single line.
>  		 * Userspace should read the hwcaps with getauxval(AT_HWCAP)
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index b1adc51..1bed772 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -326,7 +326,12 @@ static void __init hyp_mode_check(void)
>  
>  void __init smp_cpus_done(unsigned int max_cpus)
>  {
> -	pr_info("SMP: Total of %d processors activated.\n", num_online_cpus());
> +	unsigned long bogosum = loops_per_jiffy * num_online_cpus();
> +
> +	pr_info("SMP: Total of %d processors activated (%lu.%02lu BogoMIPS).\n",
> +		num_online_cpus(), bogosum / (500000/HZ),
> +		(bogosum / (5000/HZ)) % 100);

Can we drop this hunk? I don't see a pressing need to print this in
dmesg.

With those two changes:

  Acked-by: Will Deacon <will.deacon@....com>

I guess this needs Cc'ing to stable, too.

Thanks,

Will
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