[Xen-devel] the logic of burn_credits

[he qiang <qiang20102697@xxxxxxxxx>]

I am a undergraduate student and I am reading xen source code.
I can't understand the logic of the function burn_credits in xen-4.3.2/xen/common/sched_credit.c.
I think the unit of the variable delta is nanosecond and the unit of the const CSCHED_CREDITS_PER_MSEC is millisecond,
then where is the sense of the line  "val = delta * CSCHED_CREDITS_PER_MSEC + svc->residual;"?
and what does the variable  svc->start_time mean? if it means time When the vcpu was scheduled in system time
and where is the sense of the line "svc->start_time += (credits * MILLISECS(1)) / CSCHED_CREDITS_PER_MSEC;"?
thank you very much.

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