QUESTION $3$

Multiple processors need to share data quickly and efficiently to achieve high performance. One

way to do this is through shared memory. However, shared memory can present a problem when

multiple processors try to access the same memory location simultaneously. Figure Q$3$ shows

a code segment that updates a shared variable "sum" in a loop written with the OpenMP

programming model.

Figure Q$3$

$($a$)$ Explain in detail the use of OpenMP's "critical" directive to solve the shared memory

problem in an HPC system. Also, identify the problem that might occur by executing

this directive.

$[5$ marks$]$

$($b$)$ The impact of this overhead can be quantified by measuring the execution time of the

program with and without the "critical" directive. Re$-$write the program to measure the

performance impact of the "critical" directive by utilising OpenMP's built$-$in timers.

Explain in detail about your program.