Workqueue implementation in Linux Kernel - c

Question

Can any one help me to understand difference between below mentioned APIs in Linux kernel:
struct workqueue_struct *create_workqueue(const char *name);
struct workqueue_struct *create_singlethread_workqueue(const char *name);
I had written sample modules, when I try to see them using ps -aef, both have created a workqueue, but I was not able to see any difference.
I have referred to http://www.makelinux.net/ldd3/chp-7-sect-6, and according to LDD3:
If you use create_workqueue, you get a workqueue that has a dedicated thread for each processor on the system. In many cases, all those threads are simply overkill; if a single worker thread will suffice, create the workqueue with create_singlethread_workqueue instead.
But I was not able to see multiple worker threads (each for a processor).

Answer 1

Workqueues have changed since LDD3 was written.
These two functions are actually macros:
#define create_workqueue(name) \
alloc_workqueue("%s", WQ_MEM_RECLAIM, 1, (name))
#define create_singlethread_workqueue(name) \
alloc_workqueue("%s", WQ_UNBOUND | WQ_MEM_RECLAIM, 1, (name))
The alloc_workqueue documentation says:
Allocate a workqueue with the specified parameters. For detailed
information on WQ_* flags, please refer to Documentation/workqueue.txt.
That file is too big to quote entirely, but it says:
alloc_workqueue() allocates a wq. The original create_*workqueue()
functions are deprecated and scheduled for removal.
[...]
A wq no longer manages execution resources but serves as a domain for
forward progress guarantee, flush and work item attributes.

Answer 2

if(singlethread){
cwq = init_cpu_workqueue(wq, singlethread_cpu);
err = create_workqueue_thread(cwq, singlethread_cpu);
start_workqueue_thread(cwq, -1);
}else{
list_add(&wq->list, &workqueues);
for_each_possible_cpu(cpu) {
cwq = init_cpu_workqueue(wq, cpu);
err = create_workqueue_thread(cwq, cpu);
start_workqueue_thread(cwq, cpu);
}
}