Until now we used struct timespec for instr_time on all platforms but windows. Using struct timespec causes a fair bit of memory (struct timeval is 16 bytes) and runtime overhead (much more complicated additions). Instead we can convert the time to nanoseconds in INSTR_TIME_SET_CURRENT(), making the remaining operations cheaper.
Representing time as int64 nanoseconds provides sufficient range, ~292 years relative to a starting point (depending on clock source, relative to the unix epoch or the system's boot time). That'd not be sufficient for calendar time stored on disk, but is plenty for runtime interval time measurement.
On windows instr_time already is represented as cycles. It might make sense to represent time as cycles on other platforms as well, as using cycle acquisition instructions like rdtsc directly can reduce the overhead of time acquisition substantially. This could be done in a fairly localized manner as the code stands after this commit.
Because the windows and non-windows paths are now more similar, use a common set of macros. To make that possible, most of the use of LARGE_INTEGER had to be removed, which looks nicer anyway.
To avoid users of the API relying on the integer representation, we wrap the 64bit integer inside struct struct instr_time.
Author: Andres Freund Author: Lukas Fittl Author: David Geier
03023a2664 instr_time: Represent time as an int64 on all platforms
src/include/portability/instr_time.h | 162 +++++++++++++++++++----------------
1 file changed, 86 insertions(+), 76 deletions(-)