On Thu, 18 Jan 2018 10:53:37 +0900 Byungchul Park <byungchul.park@xxxxxxx> wrote: > Hello, > > This is a thing simulating a wait for an event e.g. > wait_for_completion() doing spinning instead of sleep, rather > than a spinlock. I mean: > > This context > ------------ > while (READ_ONCE(console_waiter)) /* Wait for the event */ > cpu_relax(); > > Another context > --------------- > WRITE_ONCE(console_waiter, false); /* Event */ I disagree. It is like a spinlock. You can say a spinlock() that is blocked is also waiting for an event. That event being the owner does a spin_unlock(). > > That's why I said this's the exact case of cross-release. Anyway > without cross-release, we usually use typical acquire/release > pairs to cover a wait for an event in the following way: > > A context > --------- > lock_map_acquire(wait); /* Or lock_map_acquire_read(wait) */ > /* Read one is better though.. */ > > /* A section, we suspect, a wait for an event might happen. */ > ... > lock_map_release(wait); > > > The place actually doing the wait > --------------------------------- > lock_map_acquire(wait); > lock_map_acquire(wait); > > wait_for_event(wait); /* Actually do the wait */ > > You can see a simple example of how to use them by searching > kernel/cpu.c with "lock_acquire" and "wait_for_completion". > > However, as I said, if you suspect that cpu_relax() includes > the wait, then it's ok to leave it. Otherwise, I think it > would be better to change it in the way I showed you above. I find your way confusing. I'm simulating a spinlock not a wait for completion. A wait for completion usually initiates something then waits for it to complete. This is trying to get into a critical area but another task is currently in it. It's simulating a spinlock as far as I can see. -- Steve -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
