CODEWITHSUNDEEP
cuda
duttasankha
duttasankha

Reputation: 737

How Concurrent blocks can run a single GPU streaming multiprocessor?

I was studying about the CUDA programming structure and what I felt after studying is that; after creating the blocks and threads, each of this blocks is assigned to each of the streaming multiprocessor (e.g. I am using GForce 560Ti which has14 streaming multiprocessors and so at one time 14 blocks can be assigned to all the streaming multiprocessors). But as I am going through several online materials such as this one :

http://moss.csc.ncsu.edu/~mueller/cluster/nvidia/GPU+CUDA.pdf

where it has been mentioned that several blocks can be run concurrently on one multiprocessor. I am basically very much confused with the execution of the threads and the blocks on the streaming multiprocessors. I know that the assignment of blocks and the execution of the threads are absolutely arbitrary but I would like how the mapping of the blocks and the threads actually happens so that the concurrent execution could occur.

Upvotes: 5

Views: 3636

Answers (1)

Pedro
Pedro

Reputation: 1384

The Streaming Multiprocessors (SM) can execute more than one block at a time using Hardware Multithreading, a process akin to Hyper-Threading.

The CUDA C Programming Guide describes this as follows in Section 4.2:

4.2 Hardware Multithreading

The execution context (program counters, registers, etc) for each warp processed by a multiprocessor is maintained on-chip during the entire lifetime of the warp. Therefore, switching from one execution context to another has no cost, and at every instruction issue time, a warp scheduler selects a warp that has threads ready to execute its next instruction (the active threads of the warp) and issues the instruction to those threads.

In particular, each multiprocessor has a set of 32-bit registers that are partitioned among the warps, and a parallel data cache or shared memory that is partitioned among the thread blocks.

The number of blocks and warps that can reside and be processed together on the multiprocessor for a given kernel depends on the amount of registers and shared memory used by the kernel and the amount of registers and shared memory available on the multiprocessor. There are also a maximum number of resident blocks and a maximum number of resident warps per multiprocessor. These limits as well the amount of registers and shared memory available on the multiprocessor are a function of the compute capability of the device and are given in Appendix F. If there are not enough registers or shared memory available per multiprocessor to process at least one block, the kernel will fail to launch.

Upvotes: 7

Related Questions