include/linux/timecounter.h

Source file repositories/reference/linux-study-clean/include/linux/timecounter.h

File Facts

System
Linux kernel
Corpus path
include/linux/timecounter.h
Extension
.h
Size
5299 bytes
Lines
165
Domain
Core OS
Bucket
Core Kernel Interface
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

struct cyclecounter {
	u64 (*read)(struct cyclecounter *cc);
	u64 mask;
	u32 mult;
	u32 shift;
};

/**
 * struct timecounter - layer above a &struct cyclecounter which counts nanoseconds
 *	Contains the state needed by timecounter_read() to detect
 *	cycle counter wrap around. Initialize with
 *	timecounter_init(). Also used to convert cycle counts into the
 *	corresponding nanosecond counts with timecounter_cyc2time(). Users
 *	of this code are responsible for initializing the underlying
 *	cycle counter hardware, locking issues and reading the time
 *	more often than the cycle counter wraps around. The nanosecond
 *	counter will only wrap around after ~585 years.
 *
 * @cc:			the cycle counter used by this instance
 * @cycle_last:		most recent cycle counter value seen by
 *			timecounter_read()
 * @nsec:		continuously increasing count
 * @mask:		bit mask for maintaining the 'frac' field
 * @frac:		accumulated fractional nanoseconds
 */
struct timecounter {
	struct cyclecounter *cc;
	u64 cycle_last;
	u64 nsec;
	u64 mask;
	u64 frac;
};

/**
 * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
 * @cc:		Pointer to cycle counter.
 * @cycles:	Cycles
 * @mask:	bit mask for maintaining the 'frac' field
 * @frac:	pointer to storage for the fractional nanoseconds.
 *
 * Returns: cycle counter cycles converted to nanoseconds
 */
static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
				      u64 cycles, u64 mask, u64 *frac)
{
	u64 ns = (u64) cycles;

	ns = (ns * cc->mult) + *frac;
	*frac = ns & mask;
	return ns >> cc->shift;
}

/**
 * timecounter_adjtime - Shifts the time of the clock.
 * @tc:		The &struct timecounter to adjust
 * @delta:	Desired change in nanoseconds.
 */
static inline void timecounter_adjtime(struct timecounter *tc, s64 delta)
{
	tc->nsec += delta;
}

/**
 * timecounter_init - initialize a time counter
 * @tc:			Pointer to time counter which is to be initialized/reset
 * @cc:			A cycle counter, ready to be used.
 * @start_tstamp:	Arbitrary initial time stamp.
 *
 * After this call the current cycle register (roughly) corresponds to
 * the initial time stamp. Every call to timecounter_read() increments
 * the time stamp counter by the number of elapsed nanoseconds.
 */
extern void timecounter_init(struct timecounter *tc,
			     struct cyclecounter *cc,
			     u64 start_tstamp);

/**
 * timecounter_read - return nanoseconds elapsed since timecounter_init()
 *                    plus the initial time stamp
 * @tc:          Pointer to time counter.
 *
 * In other words, keeps track of time since the same epoch as
 * the function which generated the initial time stamp.
 *
 * Returns: nanoseconds since the initial time stamp
 */
extern u64 timecounter_read(struct timecounter *tc);

/*
 * This is like cyclecounter_cyc2ns(), but it is used for computing a

Annotation

Implementation Notes