Hi, Paul,
Can you help us on WRITE_ONCE()/READ_ONCE()/barrier() usage as follows?
For some example kernel code as follows,
"
unsigned char x[16];
void writer(void)
{
memset(x, 1, sizeof(x));
/* To make memset() take effect ASAP */
barrier();
}
unsigned char reader(int n)
{
return READ_ONCE(x[n]);
}
"
where, writer() and reader() may be called on 2 CPUs without any lock.
It's acceptable for reader() to read the written value a little later.
Our questions are,
1. because it's impossible for accessing "unsigned char" to cause
tearing. So, WRITE_ONCE()/READ_ONCE()/barrier() isn't necessary for
correctness, right?
2. we use barrier() and READ_ONCE() in writer() and reader(), because we
want to make writing take effect ASAP. Is it a good practice? Or it's
a micro-optimization that should be avoided?
--
Best Regards,
Huang, Ying
