PERCPU(9)

PERCPU(9) | 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 memory 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 subsequently 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 voluntarily 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 success.
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>

January 23, 2010 | NetBSD 7.1