On Sat, 11 Jun 2005 09:14, J.A. Magallon wrote:
> On 06.10, Con Kolivas wrote:
> > The priority biasing was off by mutliplying the total load by the total
> > priority bias and this ruins the ratio of loads between runqueues. This
> > patch should correct the ratios of loads between runqueues to be
> > proportional to overall load.
>
> 2.6.12-rc6-mm1 + this patch just oopses nicely on boot.
> I did not had a digital camera handy, but the first oops that fit in the
> screen was this call chain:
>
> kernel_thread_helper
> init
> init
> do:base_setup
> usermodehelper_init
> __create_workqueue
> EIP in try_to_wake_up
>
> After this, there was another with some do_div_error calls...
>
> Something looks un-initialized the first time, or the integer arithmetic
> is wrong. I really dont like a*(b/c), I really prefer (a*b)/c. It is more
> common b/c == 0 (because b<c), than the possibility of overflowing (a*b).
>
> So I tried both. With this, it boots again:

Doh Doh DOH DOH!
I need a real swift kick up the bum. The point of the patch was to show what 
was wrong with the math, and I shouldn't have posted it without actually 
trying it.

> -		unsigned long prio_bias = rq->prio_bias / rq->nr_running;

rq->nr_running can often be 0 and rq->prio_bias by definition has to be larger 
than or equal to rq->nr_running.

> Perhaps this:
>
> 	if (idle == NOT_IDLE || rq->nr_running > 1)
>
> should be
>
> 	if (idle == NOT_IDLE && rq->nr_running > 1)

No, testing for rq->nr_running > 1 is only needed if we are balancing in an 
idle balance.

> Hope this helps, thanks.

Yes it does :\

Here is what the patch _should_ have been. (*same warnings with this patch 
about math demonstration and untested as should have been posted with the 
earlier one*)

Con