Am 05.04.2015 um 15:43 schrieb Weng Tianxiang:
> Does each core of 8-core Intel processor has an independent floating X87 unit? 

Yes. All cores are identical, each has independent resources to do x87.

> 5.2 X87 FPU INSTRUCTIONS
> The x87 FPU instructions are executed by the processor's x87 FPU. 
> These instructions operate on floating-point, integer,[..]
> 
> These instructions are divided into the following subgroups:
> data transfer, load constants, and FPU control instructions.
> 
> From above text I have a feeling that all 8 execution cores share the same X87 FPU unit.

No that's wrong. Instruction documentation describes the core itself (a single core).
Depending on the CPU model, you get multiple instances of the described core.

> Is there anyone who has real experiences with X87 FPU unit?

x87 is legacy nowadays. It is (mostly?) superseded by SSE and AVX instructions,
which have better performance and also allow for SIMD parallelism.


Hendrik vdH

Hi, 
Does each core of 8-core Intel processor has an independent floating X87 unit? 

Here are some texts from Intel latest datasheet:

Intel(R) Core(tm) i7 Processor Family for LGA2011-v3 Socket
Datasheet - Volume 1 of 2

Processor Feature Details
*Up to 8 execution cores
*Each core supports two threads (Intel(R) Hyper-Threading Technology)
*32 KB instruction and 32 KB data first-level cache (L1) for each core
*256 KB shared instruction/data mid-level (L2) cache for each core
*Up to 15 MB last level cache (LLC): up to 2.5 MB per core instruction/data last level cache (LLC), shared among all cores.

5.2 X87 FPU INSTRUCTIONS
The x87 FPU instructions are executed by the processor's x87 FPU. These instructions operate on floating-point, integer, and binary-coded decimal (BCD) operands. For more detail on x87 FPU instructions, see Chapter 8, "Programming with the x87 FPU."

These instructions are divided into the following subgroups: data transfer, load constants, and FPU control instructions.

From above text I have a feeling that all 8 execution cores share the same X87 FPU unit.

Am I right or not? 

Is there anyone who has real experiences with X87 FPU unit?

Thank you. 

Weng