Hi. I try to synchronnize thread groups at some point. The main idea is to make groups execute successively one at a time while others are just looping waiting. It looks something like this:

g_var is a RWBuffer variable, initially set to g_numGroups-1

[allow_uav_condition] do

{

if(groupID == g_var)

{

if(groupID == 0)

g_var = g_numGroups-1;

else

g_var -= 1;

break;

}

}while(true);

GroupMemoryBarrierWithGroupSync synchronizes threads within a group. I want to synchronize all threads.

I have 5 groups 32 threads each. If i increment by 2 so that only groups indexed 4, 2 and 0 are in play it works. But when 4 is reduced by 1 then group number 3 never steps in and all is looping endlessly. It is kind of wierd.

Ok, if i split it into several dispatch calls what would be better: keep the shader in one piece, separate it in several if() sections and choose the right one with cbuffer vars, changing it between dispatches or split the shader into several ones.

I think splitting would make more sense rather than branching.

Or you can use defines to effectively split the shader - either way you need to set different shaders.

If i try to apply a very basic logic, since i dont have any knowledge of this, i would say setting a shader can involve moving some code, maybe compiling it, setting some registers with constants from the code, etc. Setting a constant buffer is just setting some registers. All threads take the same pathes, based on constants. From this point of view i would prefer to change a constant buffer unless i miss some aspect i dont know about.

There is a funny thing i found. Say, there is a shader with two pathes and two dispatch calls taking those pathes. In the first path one writes some value to a buffer and in the second one just reads it back. The pathes are taken based on cbuffer variables that are switched between the calls. So if we write into a RWByteAddressBuffer on the first call the value does not survive the call, one cannot read it back, it zeroes out. I can read it back still during the first call though, so it is not like i dont set it. It is there, but then gets lost. RWStructuredBuffer seems OK. Has anyone noticed this kind of behavior?