6aa26565e6
- 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
42 lines
955 B
C
42 lines
955 B
C
#ifndef __SPINLOCK_H__
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#define __SPINLOCK_H__
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#include "kernel.h"
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typedef struct spinlock {
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atomic_t val;
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} spinlock_t;
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#ifndef CONFIG_SMP
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#define SPINLOCK_DEFINE(name)
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#define PRIVATE_SPINLOCK_DEFINE(name)
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#define SPINLOCK_DECLARE(name)
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#define spinlock_init(sl)
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#define spinlock_lock(sl)
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#define spinlock_unlock(sl)
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#else
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/* SMP */
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#define SPINLOCK_DEFINE(name) spinlock_t name;
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#define PRIVATE_SPINLOCK_DEFINE(name) PRIVATE SPINLOCK_DEFINE(name)
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#define SPINLOCK_DECLARE(name) extern SPINLOCK_DEFINE(name)
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#define spinlock_init(sl) do { (sl)->val = 0; } while (0)
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#if CONFIG_MAX_CPUS == 1
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#define spinlock_lock(sl)
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#define spinlock_unlock(sl)
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#else
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#define spinlock_lock(sl) arch_spinlock_lock((atomic_t*) sl)
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#define spinlock_unlock(sl) arch_spinlock_unlock((atomic_t*) sl)
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#endif
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#endif /* CONFIG_SMP */
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#define BKL_LOCK() spinlock_lock(&big_kernel_lock)
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#define BKL_UNLOCK() spinlock_unlock(&big_kernel_lock)
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#endif /* __SPINLOCK_H__ */
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