#Linux kernel resource locking mechanism drivers
#Linux kernel resource locking mechanism update
#Linux kernel resource locking mechanism code

On Linux, each file is associated with directory entry There is ample documentation inįor an RCU usage example, look at fs/dcache.c. Structures and interface functions are defined in include/linux/rcupdate.h. Primitives discussed thus far and should be used only if you are sure that it's the right tool for the job. Be aware that using RCU is more involved than using the The original copy is maintained until the next context switch on all CPUs toĮnsure completion of all ongoing read operations.

#Linux kernel resource locking mechanism update

They perform update operations on a copy of the data structure and The basic idea is that reader threads can execute without Performance when readers far outnumber writers. The 2.6 kernel introduced another mechanism called Read-Copy Update (RCU), which yields improved Writers protect critical regions using write_seqlock() and write_sequnlock().

} while (read_seqretry(&xtime_lock, seq)) Because of this, reader threads may discover that their entry inside a critical section has failedĪnd may need to retry: u64 get_jiffies_64(void) /* Defined in kernel/time.c */ Writer threads do not wait for readers who may be insideĪ critical section. Jiffies_64 variable discussed earlier in this chapter. This is useful if write operations on a variable far outnumber read accesses. Sequence locks or seqlocks, introduced in the 2.6 kernel, are reader-writer locks where writers are favored over The semantics of theseįunctions are similar to those of regular spinlocks. Read_lock_irqrestore(), write_lock_irqsave(), and write_lock_irqrestore(). Like regular spinlocks, reader-writer locks also have corresponding irq variants-namely, read_lock_irqsave(), This improves performance because there are usuallyįar more instances of routing table lookups than routing table updates. Threads that need to add orĭelete entries from the routing table acquire writer locks. That need to look up the routing table to forward packets request reader locks. Reader-writer lock called ipx_routes_lock protects the IPX routing table from simultaneous access.

#Linux kernel resource locking mechanism code

Look at the IPX routing code present in net/ipx/ipx_route.c for a real-life example of a reader-writer spinlock. Write_unlock(&myrwlock) /* Release lock */ Write_lock(&myrwlock) /* Acquire writer lock */ Writer spinlocks, you would write this: rwlock_t myrwlock = RW_LOCK_UNLOCKED However, if a writer thread enters a critical section, other reader or writer threads are not allowed inside. Read_unlock(&myrwlock) /* Release lock */ Read_lock(&myrwlock) /* Acquire reader lock */ Reader spinlocks are defined as follows: rwlock_t myrwlock = RW_LOCK_UNLOCKED Multiple reader threads are allowed inside a critical region simultaneously. If the usage of aĬritical section is such that separate threads either read from or write to a shared data structure, but don't doīoth, these locks are a natural fit. It seems the part dealing with RCU at the end may be what you're interested in.Īnother specialized concurrency regulation mechanism is a reader-writer variant of spinlocks.

#Linux kernel resource locking mechanism drivers

Here's a direct quote from Essential Linux Device Drivers which might be what you're looking for.