[Gllug] Programming for performance on Linux

[general_email at technicalbloke.com]

Nix wrote:
> On 14 May 2010, general said:
>   
>> I don't think L1 cache is shared, L2 cache can be though depending on
>> the architecture. IIRC Intel Core 2 Duos have a shared L2 cache common
>> to all cores
>>     
>
> No, they have a shared *L3* cache common to all cores. L1/L2 is private
> to a single core (though of course shared between hyperthreads on one
> core).
>
> e.g. on my hyperthreaded quad-core Nehalem:
>
> spindle:/sys/devices/system/cpu/cpu0/cache# for name in index*; do echo $(cat $name/type):L$(cat $name/level):$(cat $name/size):$(cat $name/shared_cpu_list); done
> Data:L1:32K:0,4
> Instruction:L1:32K:0,4
> Unified:L2:256K:0,4
> Unified:L3:8192K:0-7
>
> (this provides benefits for multithreading -- less cache bouncing if
> running several threads of the same program -- and downsides for
> multiprocessing -- the effective available cache shrinks as the number
> of simultaneously running processes not sharing cache goes up.)
>   


Really?

Quoting from http://www.intel.com/products/processor/core2duo/index.htm
> With an Intel® Core™2 Duo processor you will get performance-rich
> technologies, including up to 6MB of shared L2 cache, up to 1333 MHz
> Front Side Bus, plus these additional Intel® technologies built in: 

What am I missing here?

Roger.
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