Can someone explain the meaning of frontend and backend stalled cycles in perf stat output?

Backend
1

I’ve been experimenting with the perf stat command and I’m puzzled by two specific metrics in the results. What exactly do ‘stalled-cycles-frontend’ and ‘stalled-cycles-backend’ represent? I searched online for clarity but didn’t come across a definitive explanation. Below is an example of the output I’m seeing:

$ perf stat echo "Hello World"

Performance stats:

  0.501234 task-clock                #    0.654 CPUs used          
         0 context-switches          #    0.000 K/sec                  
         0 CPU-migrations            #    0.000 K/sec                  
       156 page-faults               #    0.311 M/sec                  
    567890 cycles                    #    1.133 GHz                    
    789012 stalled-cycles-frontend   #  138.94% frontend cycles idle   
    456789 stalled-cycles-backend    #   80.44% backend cycles idle
    678901 instructions              #    1.20  insns per cycle        
                                     #    1.16  stalled cycles per insn
    123456 branches                  #  246.304 M/sec                  
      7890 branch-misses             #    6.39% of all branches        

0.000766543 seconds time elapsed

Can anyone help clarify what these metrics indicate and why they’re significant?

2

Frontend and backend stalled cycles are crucial metrics for understanding CPU performance bottlenecks. Frontend stalls occur when the CPU struggles to fetch and decode instructions, often due to memory latency or branch mispredictions. Backend stalls happen when the CPU cannot execute instructions efficiently, usually due to resource constraints or memory access issues.

High frontend stalls might indicate poor code locality or inefficient branch prediction, while high backend stalls could suggest memory bottlenecks or insufficient execution resources. To optimize performance, consider refining code structure, improving memory access patterns, or employing parallel processing techniques.

Addressing these stalls can significantly boost your application’s efficiency and overall system performance.

3

yo those stalls are killin ur cpu efficiency man. frontend stalls? thats when ur cpu cant fetch instructions fast enuf. backend stalls? cpu’s strugglin to execute stuff. both slow things down big time. fix em by tweakin ur code structure n memory usage. trust me itll make ur system fly!

4

hey there! those stalled cycles are like traffic jams for ur CPU. frontend stalls? thats when ur CPU’s havin trouble gettin instructions. backend stalls? it’s strugglin to execute em. both can slow things way down. have u tried tweakin ur code or memory usage? might help speed things up! what kinda program r u runnin anyways?