[RFC] WLC & SED schedulers using rate limiter instead of hard coded

[Roberto Nibali <ratz@xxxxxx>]

Hi guys,

I was wondering while polishing my threshold limitation and server pool
patch, why the WLC and SED (slightely improved WLC) schedulers do not
use the ip_vs_estimator list which is running too all the time to better
adjust their ip_vs_*_dest_overhead() methods? Currently we have
following situation:

WLC
---
static inline unsigned int
ip_vs_wlc_dest_overhead(struct ip_vs_dest *dest)
{
        /*
         * We think the overhead of processing active connections is 256
         * times higher than that of inactive connections in average. (This
         * 256 times might not be accurate, we will change it later) We
         * use the following formula to estimate the overhead now:
         *                dest->activeconns*256 + dest->inactconns
         */
        return (atomic_read(&dest->activeconns) << 8) +
                atomic_read(&dest->inactconns);
}


SED
---
 * The SED algorithm attempts to minimize each job's expected delay until
 * completion. The expected delay that the job will experience is
 * (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of
 * jobs on the the ith server and Ui is the fixed service rate (weight) of
 * the ith server. The SED algorithm adopts a greedy policy that each does
 * what is in its own best interest, i.e. to join the queue which would
 * minimize its expected delay of completion.

static inline unsigned int
ip_vs_sed_dest_overhead(struct ip_vs_dest *dest)
{
        /*
         * We only use the active connection number in the cost
         * calculation here.
         */
        return atomic_read(&dest->activeconns) + 1;
}

I wonder if adding the stats of the rate estimator would help fighting
load imbalance more sharply? OTOH load imbalance is can be balanced out
too quickly resulting in resonance catastrophy :).

Just wondering and pondering ...

Regards,
Roberto Nibali, ratz
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