[haiku-development] Writing Device Drivers - CRAM - Ticket Locking
- From: Earl Pottinger <earl_colby_pottinger@xxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Fri, 19 Aug 2011 19:13:58 -0700 (PDT)
The last few times I posted questions I did not receive any replies because
everybody was getting busy preparing for the release of Alpha-3. I hope
somebody has the time to help me with my questions at this time.
After a lot of work insuring read/write/flush commands are executed in the
order they were called I seemed to have recreated Ticket-Locking, however
ticket-locking requires a counter that is incremented atomicly.
The Atomic_Add() function documented in BeOS is only 32 bits in size. However,
a large drive (1TB or greater) could easily have more than 2^32 operations done
to it between resets. To be safe I need a 64 bit counter.
Is there a 64 bit Atomic_Add() function in Haiku?????
At present I emulate an atomic 64 bit counter with the following code:
int64 ticket_counter; // Counter is a global variable.
int64 Increment_Counter() { // Increments the counter and returns value thru
the stack. aquire_sem(counter_sem); ticket_counter++;
temp_counter = ticket_counter; release_sem(counter_sem); return
temp_counter; }
Should I use spinlocks instead of semaphores for this????
Should I be disabling interrupts only with spin-locks or will disabling
interrupts work with semaphores as well????
What is the overhead of spinlocks vs semaphores, and enabling/disabling
interrupts anyway?
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