minix/kernel/spinlock.h
Tomas Hruby 6aa26565e6 SMP - Big kernel lock (BKL)
- to isolate execution inside kernel we use a big kernel lock
  implemented as a spinlock

- the lock is acquired asap after entering kernel mode and released as
  late as possible. Only one CPU as a time can execute the core kernel
  code

- measurement son real hw show that the overhead of this lock is close
  to 0% of kernel time for the currnet system

- the overhead of this lock may be as high as 45% of kernel time in
  virtual machines depending on the ratio between physical CPUs
  available and emulated CPUs. The performance degradation is
  significant
2010-09-15 14:10:03 +00:00

41 lines
955 B
C

#ifndef __SPINLOCK_H__
#define __SPINLOCK_H__
#include "kernel.h"
typedef struct spinlock {
atomic_t val;
} spinlock_t;
#ifndef CONFIG_SMP
#define SPINLOCK_DEFINE(name)
#define PRIVATE_SPINLOCK_DEFINE(name)
#define SPINLOCK_DECLARE(name)
#define spinlock_init(sl)
#define spinlock_lock(sl)
#define spinlock_unlock(sl)
#else
/* SMP */
#define SPINLOCK_DEFINE(name) spinlock_t name;
#define PRIVATE_SPINLOCK_DEFINE(name) PRIVATE SPINLOCK_DEFINE(name)
#define SPINLOCK_DECLARE(name) extern SPINLOCK_DEFINE(name)
#define spinlock_init(sl) do { (sl)->val = 0; } while (0)
#if CONFIG_MAX_CPUS == 1
#define spinlock_lock(sl)
#define spinlock_unlock(sl)
#else
#define spinlock_lock(sl) arch_spinlock_lock((atomic_t*) sl)
#define spinlock_unlock(sl) arch_spinlock_unlock((atomic_t*) sl)
#endif
#endif /* CONFIG_SMP */
#define BKL_LOCK() spinlock_lock(&big_kernel_lock)
#define BKL_UNLOCK() spinlock_unlock(&big_kernel_lock)
#endif /* __SPINLOCK_H__ */