Re: CPUs and processes not evenly assigned?!

[christos%astron.com@localhost (Christos Zoulas)]

In article <alpine.DEB.2.00.1611102238460.6429%inya.fehu.org@localhost>,
Hubert Feyrer  <hubert%feyrer.de@localhost> wrote:
>On Thu, 10 Nov 2016, Michael van Elst wrote:
>>>> Can you try this?
>>
>>> Tried it, and it seems to help with both 2 and 4 CPUs.
>>> Codebase: -current
>>
>> Great, so the problem was just the rounding error.
>
>Yes. I've also played with it a bit more, and the "stealing" of processes 
>between CPUs seems to get less with the factor of r_mcount, e.g. with 4* 
>below I see less movement of processes on a 4-CPU system as shown in the 
>patch below.
>
>Maybe this should be made a sysctl or depend on the number of CPUs?
>
>
>  - Hubert
>
>
>
>--- sys/kern/kern_runq.c.orig   2016-11-10 21:11:10.000000000 +0000
>+++ sys/kern/kern_runq.c
>@@ -534,7 +534,9 @@ sched_balance(void *nocallout)
>                 ci_rq = ci->ci_schedstate.spc_sched_info;
>
>                 /* Average count of the threads */
>-               ci_rq->r_avgcount = (ci_rq->r_avgcount + ci_rq->r_mcount) >> 1;
>+               ci_rq->r_avgcount = (ci_rq->r_avgcount +
>+                       4*ci_rq->r_mcount
>+                       ) /2;
>
>                 /* Look for CPU with the highest average */
>                 if (ci_rq->r_avgcount > highest) {

I think that the code is wrong here; I think it should be using r_count...

		u_int totcount = ci_rq->r_count + ci_rq->r_mcount;
		ci_rq->r_avgcount = totcount >> 1;
		/* Look for CPU with the highest total */
		if (totcount > highest) {
			hci = ci;
			highest = totcount;
		}

Why avgcount is kept anyway?

christos