Intel® Quartus® Prime Software
Intel® Quartus® Prime Design Software, Design Entry, Synthesis, Simulation, Verification, Timing Analysis, System Design (Platform Designer, formerly Qsys)
Announcements
Intel Support hours are Monday-Fridays, 8am-5pm PST, except Holidays. Thanks to our community members who provide support during our down time or before we get to your questions. We appreciate you!

Need Forum Guidance? Click here
Search our FPGA Knowledge Articles here.
15547 Discussions

how to understand burst sizes info from profiler

Altera_Forum
Honored Contributor II
836 Views

hi, 

 

The profiler is showing me the following measurements for the read on the "K_contributors" global arg: 

 

Bandwidth: 0.1 MB/s, 100 % efficiency 

Average Burst Size: 2.0 

(Max Burst size: 16 ) 

 

 

// THIS IS A SINGLE WORK-ITEM KERNEL# define MAX_CONTRIBUTORS 8128 void Krnl_IntraE(... __global const char3* restrict K_contributors, ) { __local char3 localcache ; for (ushort i=0; i<MAX_CONTRIBUTORS; i++) { localcache = K_contributors ; } ... }  

 

As the loop-index "i" is increased consecutively, I expected larger burst sizes than 2. 

is there any explanation for this?
0 Kudos
2 Replies
Altera_Forum
Honored Contributor II
81 Views

You should unroll the loop so that the compiler would infer a wider port to memory, allowing for larger burst size. There is little to no runtime coalescing done for single work-item kernels and hence, you should not expect a large burst size without unrolling, just because the accesses are consecutive.

Altera_Forum
Honored Contributor II
81 Views

1. Why Bandwidth is 0.1MB/s??Is there something wrong with profiler? I also encounter this problem in quartus 17.0 

 

2. I have my kernel code like 

 

typedef struct{ 

float a[20]; 

}A 

 

__kernel foo(__global *A data){ 

A localdata[100]; 

for(i=0;i<100;i++){ 

localdata[i]=data[i+index]; 

 

I expect every memory access will bust coalescing read global memory for 20 float, so Average Burst Size suppose larger than 1. 

but in profiler Average Burst Size shows only 4~6. how to increase my access efficiency?
Reply