[Xen-devel] credit scheduler: the policy of credit assignment

[Hirokazu Takahashi <taka@xxxxxxxxxxxxx>]

Hi Emmanuel,

I looked into the code of the credit scheduler and one question
has come up.

I'm not sure whether it is your intention that once the value of
credit_balance, which is the sum of credit of all domains on Xen,
goes to zero it may be stuck at zero. It will happen all of them
are cpu intensive domains and some of them turn into idle.

Every 30 msec, the credit scheduler gives them csched_priv.credit
milliseconds --- 30 msec * number of physical cpus ---. 30 msec later,
you will find they have consumed all of the time they gave, which
leads the value of credit_balance will keep zero. This means some
domains are assigned credit with negative value every time.

I know even in this case it will be balanced between domains
based on the weights but it would take quite long time to be balanced.
I feel the scheduler should give each domains larger credit than now
when credit_balance is small.

Am I something wrong about this?

Thanks,
Hirokazu Takahashi.



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