linux-kernel - Re: turbostat-17.06.23 floating point exception

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Date:   Thu, 18 Oct 2018 18:27:52 -0700
From:   Solio Sarabia <solio.sarabia@...el.com>
To:     Len Brown <lenb@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        shiny.sebastian@...el.com
Subject: Re: turbostat-17.06.23 floating point exception

On Fri, Oct 12, 2018 at 07:03:41PM -0400, Len Brown wrote:
> > Why would the cpu topology report 0 cpus?  I added a debug entry to
> > cpu_usage_stat and /proc/stat showed it as an extra column.  Then
> > fscanf parsing in for_all_cpus() failed, causing the SIGFPE.
> >
> > This is not an issue. Thanks.
> 
> Yes, it is true that turbostat doesn't check for systems with 0 cpus.
> I'm curious how you provoked the kernel to claim that.  If it is
> something others might do, we can have check for it and gracefully
> exit.

source/tools/power/x86/turbostat/turbostat.c
int for_all_proc_cpus(int (func)(int))
{
    retval = fscanf(fp, "cpu %*d %*d %*d %*d %*d %*d %*d %*d %*d %*d\n");
    ^
    This fails due to an extra debug entry in /proc/stat
    (total of 11 columns).  I was measuring time in a hot
    function and decided to add this time in an extra
    cpu_usage_stat. This was an experiment though.

Thanks,
-S.