Re: Dmesg info interpretation

On 12/01/2015 04:15 AM, Patrick AGRAIN wrote:
> Hello all,
>  
> Please forgive me in advance for this (meaby) newbie-like question, but as I’m new in this topic, I wish to clarify some vocabulary.
>  
> From _https://perf.wiki.kernel.org/index.php/Tutorial_, I saw that they give following example:
> *Processor * 	*Generic counters * 	*Fixed counters *
> Intel Core 	2 	3
> Intel Nehalem 	4 	3
> 
> Referring the dmesg output of my system :
> <...>
> CPU0: Intel(R) Pentium(R) CPU G3220 @ 3.00GHz stepping 03
> Performance Events: no PEBS fmt2+, generic architected perfmon, Intel PMU driver.
> ... version:                3
> ... bit width:              48
> ... generic registers:      8
> ... value mask:             0000ffffffffffff
> ... max period:             000000007fffffff
> ... fixed-purpose events:   3
> ... event mask:             00000007000000ff
> Brought up 1 CPUs
> <...>
> Would it be correct to write that my system:
> 
>   * Has 8 generic counters.
>   * Has 3 fixed counters.
>   * Counters are 48-bits wide.
> 
> Thanks to correct me if I’m wrong.
> Kind regards,
> Patrick Agrain

Hi Patrick,

A number of the Intel processors allow two logical processors on a physical processor.  In these cases perf give each logical processor half the pmu counters.  Thus, rather than 8 counters per CPU there are 4 counters available.  You can check this by looking for "ht" in the "flags:" line of the /proc/info output.  Looking at the Intel Penium CPUG3220 information at http://ark.intel.com/products/77773/Intel-Pentium-Processor-G3220-3M-Cache-3_00-GHz , it has two physical cores and two threads, so it doesn't look like it does the threading.  Perf shouldn't have to split the pmu counters between logical processors if there is no hyperthreading.

-Will

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