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PERCPU(9)		 BSD Kernel Developer's Manual		     PERCPU(9)

NAME
     percpu, percpu_alloc, percpu_free, percpu_getref, percpu_putref,
     percpu_foreach — per-CPU storage allocator

SYNOPSIS
     #include <sys/percpu.h>

     typedef void (*percpu_callback_t)(void *, void *, struct cpu_info *);

     percpu_t *
     percpu_alloc(size_t size);

     void
     percpu_free(percpu_t *pc, size_t size);

     void *
     percpu_getref(percpu_t *pc);

     void
     percpu_putref(percpu_t *pc);

     void
     percpu_foreach(percpu_t *pc, percpu_callback_t cb, void *arg);

DESCRIPTION
     The machine-independent percpu interface provides per-CPU, CPU-local mem‐
     ory reservations to kernel subsystems.  percpu_alloc(size) reserves on
     each CPU an independent memory region of size bytes that is local to that
     CPU, returning a handle (percpu_t) to those regions.  A thread may subse‐
     quently ask for a pointer, p, to the region held by the percpu_t on the
     thread's current CPU.  Until the thread relinquishes the pointer, or vol‐
     untarily sleeps, the thread may read or write the region at p without
     causing interprocessor memory synchronization.

FUNCTIONS
     percpu_alloc(size)
	      Call this in thread context to allocate size bytes of local
	      storage on each CPU.  The storage is initialized with zeroes.
	      Treat this as an expensive operation.  percpu_alloc() returns
	      NULL on failure, and a handle for the per-CPU storage on suc‐
	      cess.

     percpu_free(pc, size)
	      Call this in thread context to return to the system the per-CPU
	      storage held by pc.  size should match the size passed to
	      percpu_alloc().  When percpu_free() returns, pc is undefined.
	      Treat this as an expensive operation.

     percpu_getref(pc)
	      Disable preemption and return a pointer to the storage held by
	      pc on the local CPU.  Use percpu_getref() in either thread or
	      interrupt context.  Follow each percpu_getref() call with a
	      matching call to percpu_putref().

     percpu_putref(pc)
	      Indicate that the thread is finished with the pointer returned
	      by the matching call to percpu_getref().	Re-enables preemption.

     percpu_foreach(pc, cb, arg)
	      On each CPU, for ci the corresponding struct cpu_info * and p
	      the CPU-local storage held by pc, run (*cb)(p, arg, ci).	Call
	      this in thread context.  cb should be non-blocking and fast.  Do
	      not rely on cb to be run on the CPUs in any particular order.

CODE REFERENCES
     The percpu interface is implemented within the file
     sys/kern/subr_percpu.c.

SEE ALSO
     atomic_ops(3), kmem(9), pcq(9), pool_cache(9), xcall(9)

HISTORY
     The percpu interface first appeared in NetBSD 6.0.

AUTHORS
     YAMAMOTO Takashi ⟨yamt@NetBSD.org⟩

BSD			       January 23, 2010				   BSD

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