A warp or wavefront is a logical unit in GPU kernel scheduling - the largest set of threads within the grid which are (logically) instruction-locked and always synchronized with each other..
If I start my kernel with a grid whose blocks have dimensions:
dim3 block_dims(16,16);
How are the grid blocks now split into warps? Do the first two rows of such a block form one warp, or the first two columns, or is this arbitrarily-ordered?…
I have GeForce GTX460 SE, so it is: 6 SM x 48 CUDA Cores = 288 CUDA Cores.
It is known that in one Warp contains 32 threads, and that in one block simultaneously (at a time) can be executed only one Warp.
That is, in a single multiprocessor (SM) can…
Note: This question is specific to nVIDIA Compute Capability 2.1 devices. The following information is obtained from the CUDA Programming Guide v4.1:
In compute capability 2.1 devices, each SM has 48 SP (cores)
for integer and floating point…
After read this post on CUDA Developer Blog I am struggling to understand when is safe\correct use __activemask() in place of __ballot_sync().
In section Active Mask Query, the authors wrote:
This is incorrect, as it would result in partial sums…
In generalizing a kernel thats shifts the values of a 2D array one space to the right (wrapping around the row boundaries), I have come across a warp synchronization problem. The full code is attached and included below.
The code is meant to work…
I am wondering if the warp scheduling order of a CUDA application is deterministic.
Specifically I am wondering if the ordering of warp execution will stay the same with multiple runs of the same kernel with the same input data on the same device.…
The following code sums every 32 elements in an array to the very first element of each 32 element group:
int i = threadIdx.x;
int warpid = i&31;
if(warpid < 16){
s_buf[i] += s_buf[i+16];__syncthreads();
s_buf[i] +=…
Edit: I've filed this as a bug at https://developer.nvidia.com/nvidia_bug/3711214.
I'm writing a numerical simulation program that is giving subtly-incorrect results in Release mode, but seemingly correct results in Debug mode. The original program…
In the cuda examples, e.g. here, __match_all_sync __match_any_sync is used.
Here is an example where a warp is split into multiple (one or more) groups that each keep track of their own atomic counter.
// increment the value at ptr by 1 and return…
In CUDA 9, nVIDIA seems to have this new notion of "cooperative groups"; and for some reason not entirely clear to me, __ballot() is now (= CUDA 9) deprecated in favor of __ballot_sync(). Is that an alias or have the semantics changed?
... similar…
I am a bit confused with how memory access issued by a warp is affected by FP64 data.
A warp always consists of 32 threads regardless if these threads are doing FP32 or FP64 calculations. Right?
I have read that each time a thread in a warp tries…
From the CUDA Prgramming Guide:
[Warp shuffle functions] exchange a variable between threads within a
warp.
I understand that this is an alternative to shared memory, thus it's being used for threads within a warp to "exchange" or share values.…
Problem
Compute a per-warp histogram of sorted sequence of numbers held by individual threads in a warp.
Example:
lane: 0123456789... 31
val: 222244455777799999 ..
The result must be held by N lower threads in a warp (where N is the…
Let's say I have an OpenGL compute shader with local_size=8*8*8. How do the invocations map to nVidia GPU warps? Would invocations with the same gl_LocalInvocationID.x be in the same warp? Or y? Or z? I don't mean all invocations, I just mean…
A warp is 32 threads. Does the 32 threads execute in parallel in a Multiprocessor?
If 32 threads are not executing in parallel then there is no race condition in the warp.
I got this doubt after going through the some examples.
