Re: [Xen-devel] [PATCH] Supporting reading of system information from BIOS.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/10/14 05:44, Rita Sinha wrote:

Thanks for having a stab at this.  Some comments inline

> This patch is in response to 
> http://wiki.xenproject.org/wiki/Outreach_Program_Projects#CPU.2FRAM.2FPCI_diagram_tool
>  project for applying to OPW-Round9.It adds support for reading system 
> architecture information from BIOS rather than from sysfs and proc interfaces 
> since in a virtualisation enviroment, some of this information is no longer 
> accurate, particularly any information based around numbers of cpus.

Would you mind formatting this to 80 columns wide?

Generally speaking, submission of patches need a Signed-off-by: tag.

> ---
>  dmidecode.pl | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
>  create mode 100644 dmidecode.pl
>
> diff --git a/dmidecode.pl b/dmidecode.pl
> new file mode 100644
> index 0000000..76fdf78
> --- /dev/null
> +++ b/dmidecode.pl
> @@ -0,0 +1,51 @@
> +#!/usr/bin/perl
> +
> +# dmidecode.pl - a script to read the system architecture information
> +# directly from the BIOS.  Only for Linux.
> +#
> +# Rita Sinha (rita.sinha89@xxxxxxxxx)
> +# OPW Program-Round9
> +# 14/10/14
> +
> +`id -u` == 0 || die "must be run as root";
> +
> +open(DmiFh, "/usr/sbin/dmidecode |") or
> +  die "problem running dmidecode";
> +$DmiNumProcs = 0;
> +$DmiNumSockets = 0;
> +while(<DmiFh>)
> +  {
> +    next unless /Central Processor/;
> +    # We've found a processor (or at least a socket), keep going
> +    while(<DmiFh>)
> +     {
> +       # Keep walking the dmidecode output to find out if
> +       # the socket has a processor in it.
> +       last if /^Handle/;
> +       next unless /Status/;
> +       $DmiNumSockets += 1;
> +       /Populated/ and $DmiNumProcs += 1;
> +       last;
> +     }
> +  }
> +close DmiFh;
> +
> +open(CpuInfoFh, "/proc/cpuinfo") || die "failed to open /proc/cpuinfo!";
> +$CpuInfoNumProcs = 0;
> +while(<CpuInfoFh>)
> +  {
> +    next unless /^processor.*:/;
> +    ($CpuInfoNumProcs) += (/^processor.*: (\d+)/);
> +  }
> +close CpuInfoFh;
> +
> +if ( $DmiNumProcs != $CpuInfoNumProcs )
> +  {
> +    print "Warning: dmidecode reports $DmiNumProcs processors, kernel 
> reports $CpuInfoNumProcs processors.\n";
> +  }
> +
> +if ( $DmiNumProcs != $DmiNumSockets )
> +  {
> +    print "Info: dmidecode reports $DmiNumSockets cpu sockets, but only 
> $DmiNumProcs processors.\n";
> +  }
> +

Running this script in dom0 yields:

[root@fusebot ~]# ./dmidecode.pl
Warning: dmidecode reports 1 processors, kernel reports 4 processors.

This is a Xeon E3-1240 v3 system where dom0 has 4 vcpus.

Under Xen, each vcpu appears as a separate processor, which is why
/proc/cpuinfo and dmidecode disagree about the processor count.  This
also goes to show that /proc/cpuinfo only sees the virtual layout, not
the physical layout.


I think it might be worth starting with a design of the first task we
discussed, including the indented source of the information to be used.

~Andrew


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