linux-stable/include/linux/sched_clock.h

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/* SPDX-License-Identifier: GPL-2.0-only */
ARM: sched_clock: provide common infrastructure for sched_clock() Provide common sched_clock() infrastructure for platforms to use to create a 64-bit ns based sched_clock() implementation from a counter running at a non-variable clock rate. This implementation is based upon maintaining an epoch for the counter and an epoch for the nanosecond time. When we desire a sched_clock() time, we calculate the number of counter ticks since the last epoch update, convert this to nanoseconds and add to the epoch nanoseconds. We regularly refresh these epochs within the counter wrap interval. We perform a similar calculation as above, and store the new epochs. We read and write the epochs in such a way that sched_clock() can easily (and locklessly) detect when an update is in progress, and repeat the loading of these constants when they're known not to be stable. The one caveat is that sched_clock() is not called in the middle of an update. We achieve that by disabling IRQs. Finally, if the clock rate is known at compile time, the counter to ns conversion factors can be specified, allowing sched_clock() to be tightly optimized. We ensure that these factors are correct by providing an initialization function which performs a run-time check. Acked-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com> Tested-by: Will Deacon <will.deacon@arm.com> Tested-by: Mikael Pettersson <mikpe@it.uu.se> Tested-by: Eric Miao <eric.y.miao@gmail.com> Tested-by: Olof Johansson <olof@lixom.net> Tested-by: Jamie Iles <jamie@jamieiles.com> Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-12-15 19:23:07 +00:00
/*
* sched_clock.h: support for extending counters to full 64-bit ns counter
*/
#ifndef LINUX_SCHED_CLOCK
#define LINUX_SCHED_CLOCK
ARM: sched_clock: provide common infrastructure for sched_clock() Provide common sched_clock() infrastructure for platforms to use to create a 64-bit ns based sched_clock() implementation from a counter running at a non-variable clock rate. This implementation is based upon maintaining an epoch for the counter and an epoch for the nanosecond time. When we desire a sched_clock() time, we calculate the number of counter ticks since the last epoch update, convert this to nanoseconds and add to the epoch nanoseconds. We regularly refresh these epochs within the counter wrap interval. We perform a similar calculation as above, and store the new epochs. We read and write the epochs in such a way that sched_clock() can easily (and locklessly) detect when an update is in progress, and repeat the loading of these constants when they're known not to be stable. The one caveat is that sched_clock() is not called in the middle of an update. We achieve that by disabling IRQs. Finally, if the clock rate is known at compile time, the counter to ns conversion factors can be specified, allowing sched_clock() to be tightly optimized. We ensure that these factors are correct by providing an initialization function which performs a run-time check. Acked-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com> Tested-by: Will Deacon <will.deacon@arm.com> Tested-by: Mikael Pettersson <mikpe@it.uu.se> Tested-by: Eric Miao <eric.y.miao@gmail.com> Tested-by: Olof Johansson <olof@lixom.net> Tested-by: Jamie Iles <jamie@jamieiles.com> Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-12-15 19:23:07 +00:00
#ifdef CONFIG_GENERIC_SCHED_CLOCK
/**
* struct clock_read_data - data required to read from sched_clock()
*
* @epoch_ns: sched_clock() value at last update
* @epoch_cyc: Clock cycle value at last update.
* @sched_clock_mask: Bitmask for two's complement subtraction of non 64bit
* clocks.
* @read_sched_clock: Current clock source (or dummy source when suspended).
* @mult: Multipler for scaled math conversion.
* @shift: Shift value for scaled math conversion.
*
* Care must be taken when updating this structure; it is read by
* some very hot code paths. It occupies <=40 bytes and, when combined
* with the seqcount used to synchronize access, comfortably fits into
* a 64 byte cache line.
*/
struct clock_read_data {
u64 epoch_ns;
u64 epoch_cyc;
u64 sched_clock_mask;
u64 (*read_sched_clock)(void);
u32 mult;
u32 shift;
};
extern struct clock_read_data *sched_clock_read_begin(unsigned int *seq);
extern int sched_clock_read_retry(unsigned int seq);
extern void generic_sched_clock_init(void);
extern void sched_clock_register(u64 (*read)(void), int bits,
unsigned long rate);
#else
static inline void generic_sched_clock_init(void) { }
static inline void sched_clock_register(u64 (*read)(void), int bits,
unsigned long rate)
{
}
#endif
ARM: sched_clock: provide common infrastructure for sched_clock() Provide common sched_clock() infrastructure for platforms to use to create a 64-bit ns based sched_clock() implementation from a counter running at a non-variable clock rate. This implementation is based upon maintaining an epoch for the counter and an epoch for the nanosecond time. When we desire a sched_clock() time, we calculate the number of counter ticks since the last epoch update, convert this to nanoseconds and add to the epoch nanoseconds. We regularly refresh these epochs within the counter wrap interval. We perform a similar calculation as above, and store the new epochs. We read and write the epochs in such a way that sched_clock() can easily (and locklessly) detect when an update is in progress, and repeat the loading of these constants when they're known not to be stable. The one caveat is that sched_clock() is not called in the middle of an update. We achieve that by disabling IRQs. Finally, if the clock rate is known at compile time, the counter to ns conversion factors can be specified, allowing sched_clock() to be tightly optimized. We ensure that these factors are correct by providing an initialization function which performs a run-time check. Acked-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com> Tested-by: Will Deacon <will.deacon@arm.com> Tested-by: Mikael Pettersson <mikpe@it.uu.se> Tested-by: Eric Miao <eric.y.miao@gmail.com> Tested-by: Olof Johansson <olof@lixom.net> Tested-by: Jamie Iles <jamie@jamieiles.com> Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-12-15 19:23:07 +00:00
#endif