[Omp] Still on the barrier

[Shengyan Hong]

Every OMP member,
           In my experiment, I do not add the "C" comment labels to the 
lines between CALL MAGIC_BRK_SIM_MIDDLE() and CALL MAGIC_BRK_SIM_STOP().
                                            Shengyan Hong


On Sun, 11 Mar 2007, Eugene Loh wrote:

> Shengyan Hong wrote:
>
>>         Suppose there are 8 processors. Each has different frequencies and 
>> L1 cache latencies. For example, Cpu1 has 1.1 GHz and its L1 cache latency 
>> is 2 cycle.
>>         Suppose there are 8 threads in one benchmark. Suppose there is one 
>> barrier for these 8 threads. Suppose these 8 threads are divided into the 8 
>> processors.  Now I want to utilize the simics to test the idle time in the 
>> barrier for these 8 processors.
>>         I choose the benchmark FT.  I think that the code should be 
>> parallelized, so I choose the code as below:
>> !$omp parallel do default(shared) private(i,j,k)
>>       do k = 1, d3
>>          do j = 1, d2
>>             do i = 1, d1
>>                u0(i,j,k) = 0.d0
>>                u1(i,j,k) = 0.d0
>>                indexmap(i,j,k) = 0.d0
>>             end do
>>          end do
>>       end do
>> 
>>       return
>>       end
>> And change the code to be:
>> !$omp parallel do default(shared) private(i,j,k)
>>       do k = 1, d3
>> C       TID = OMP_GET_THREAD_NUM()
>> C       PRINT *, 'thread = ', TID
>> C       print *, "March 9"
>>        CALL MAGIC_BRK_SIM_START()
>>          do j = 1, d2
>>             do i = 1, d1
>>                u1(i,j,k) = u0(i,j,k)*ex(t*indexmap(i,j,k))
>>             end do
>>          end do
>> C       print *, "Before barrier"
>>        CALL MAGIC_BRK_SIM_MIDDLE()
>> C       !$OMP BARRIER
>> C       print *, "After barrier"
>>        CALL MAGIC_BRK_SIM_STOP()
>>        end do
>>      Now I get the idle time by using MAGIC_BRK_SIM_MIDDLE() and 
>> MAGIC_BRK_SIM_STOP. But each processor has the same idle time 6 cycles.
>> 
> I'm not sure I understand this.  Everything between SIM_MIDDLE and SIM_STOP 
> is commented out.  So, there is nothing to time.  The 6 cycles must reflect 
> how long it takes to get two consecutive timestamps.
>
> How about moving the SIM_STOP statement to after the last "end do"?
>
>> Besides, I test the execution time by using MAGIC_BRK_SIM_START() and 
>> MAGIC_BRK_SIM_MIDDLE(). And each processor has different execution time. 
>> But no too different. For example, 1.7821*10^5 and 1.78345*10^5.
>>      Since you tell me that barrier can not be added into the parallel 
>> region. Now can you tell me where I can add the barrier. I think that the 
>> place of the code should have 8 threads. Right? To the end, how can I use 
>> barrier in the fortran code? Thank you very much.
>> 
> Again, don't worry about the barrier.  Just move the final timestamp to after 
> the last "end do".
>