Peter Teoh wrote:
Thank you for your reply Sitsofe. I hope you will allow me to share with the Kernelnewbies team as well.
Of course.
To rephrase my question: In a standard x86 hardware system, we have hardware clock source from APIC timer, ACPI timer, and then old 8253 PIT timer. So my question the different API listed above uses which hardware as the source of clocking? Then there is another HPET timer - is it synonymous to one of the above timer?
Just after start up the kernel decides which hardware clock source it deems to be the best after tests (the order on x86 from most to least prefered is roughly HPET, ACPI, TSC, PIT) and goes on to only use that (after calibrating various bits). All timer events will then be generated from this one source (unless the kernel suspects it has gone bad at which point it will switch). There are several interfaces creating events to fire off at points in the future but underneath they are running off the same source that was decided at boot.
HPET hardware is "new" and is not synonymous to the APIC/ACPI, PIT or TSC hardware.
There seems to be a good treatment of timers in the Understanding the Linux Kernel, Third Edition book (see the chapter on Timing Measurements).
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