On 12/21/2016 10:46 AM, Paul Gilmartin wrote:
How does ECTG do that? Is there information in control registers supporting it?
Does it work likewise on systems other than z/OS, such as Linux? VM guests?
The high level answer is that ECTG atomically fetches 8 bytes of storage
from one location, PSADTSAV for z/OS, and subtracts the current CPU
timer value from it and loads 8 bytes from a second location, TCBTTIME
for z/OS, and loads a third value, which is the type of processor (GCP,
zIIP, zAAP) for z/OS. Using these atomically obtained values the
current CPU time can then be calculated. The calculations are *not*
something to be attempted in application code as proper adjustments have
to be made if all CP types do not run at the same speed.
If appropriate information was saved at dispatch time by other operating
systems then ECTG could be used there as well.
Regards,
Greg
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