Robert Wisniewski <[EMAIL PROTECTED]> wrote:
>
> modify_val_spin()
> {
> acquire_spin_lock()
> // calculate some_value based on global_val
> // for example c=global_val; if (c%0) some_value=10; else some_value=20;
> global_val = global_val + some_value
> release_spin_lock()
> }
>
> modify_val_atomic()
> {
> do
> // calculate some_value based on global_val
> // for example c=global_val; if (c%0) some_value=10; else some_value=20;
> global_val = global_val + some_value
> while (compare_and_store(global_val, , ))
> }
>
> What's the difference. The deal is if two processes execute this code
> simultaneously and one gets interrupted in the middle of modify_val_spin,
> then the other wastes its entire quantum spinning for the lock. In the
> modify_val_atomic if one process gets interrupted, no problem, the other
> process can proceed through, then when the first one runs again the CAS
> will fail, and it will go around the loop again.
One could use spin_lock_irq(). The performance would be similar.
> Now imagine it was the kernel involved...
Or are you saying that userspace does the above as well?
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