[RFC PATCH v2 2/2] ARM: kernel: update cpuinfo to print all online CPUs features

[Lorenzo Pieralisi]

On Fri, Nov 16, 2012 at 08:42:13PM +0000, Nicolas Pitre wrote:
> On Fri, 16 Nov 2012, Nicolas Pitre wrote:
> 
> > On Fri, 16 Nov 2012, Lorenzo Pieralisi wrote:
> > 
> > > Currently, reading /proc/cpuinfo provides userspace with CPU ID of
> > > the CPU carrying out the read from the file. This is fine as long as all
> > > CPUs in the system are the same. With the advent of big.LITTLE and
> > > heterogenous ARM systems this approach provides user space with incorrect
> > > bits of information since CPU ids in the system might differ from the one
> > > provided by the CPU reading the file.
> > > 
> > > This patch updates the cpuinfo show function so that a read from
> > > /proc/cpuinfo prints HW information for all online CPUs at once, mirroring
> > >  x86 behaviour.
> > > 
> > > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> > 
> > Acked-by: Nicolas Pitre <nico at linaro.org>
> 
> Sorry, let me take this back.  There are a few issues with the output.
> 
> First, the "processor" line is doubled for each core.  If glibc actually 
> looks at those lines to determine the number of CPUs like the nearby 
> comment says then it'll get twice the actual number of processors.
> 
> And then, there is an annoying empty line between the BogoMIPS line and 
> the rest of the information for each core.
> 
> So, I'd suggest folding this into your patch, with my ACK of course.
> 
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 53e532704c..bfa673de9e 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -859,18 +859,18 @@ static int c_show(struct seq_file *m, void *v)
>  	u32 cpuid;
>  
>  	for_each_online_cpu(i) {
> -		cpuid = is_smp() ? per_cpu(cpu_data, i).cpuid : read_cpuid_id();
> -		seq_printf(m, "Processor\t: %s rev %d (%s)\n",
> -			   cpu_name, cpuid & 15, elf_platform);
> -
> -#if defined(CONFIG_SMP)
>  		/*
>  		 * glibc reads /proc/cpuinfo to determine the number of
>  		 * online processors, looking for lines beginning with
>  		 * "processor".  Give glibc what it expects.
>  		 */
>  		seq_printf(m, "processor\t: %d\n", i);
> -		seq_printf(m, "BogoMIPS\t: %lu.%02lu\n\n",
> +		cpuid = is_smp() ? per_cpu(cpu_data, i).cpuid : read_cpuid_id();
> +		seq_printf(m, "model name\t: %s rev %d (%s)\n",
> +			   cpu_name, cpuid & 15, elf_platform);

Ok, but for sake of precision if this is a problem, it is a problem
even for the current kernel right ? If we consider the line starting
with "Processor", we would end up parsing one CPU more than we should.

I will apply your changes.

Thanks,
Lorenzo