Re: [PATCH V2] sched: Improve load balancing in the presence of idle CPUs

[Jason Low <jason.low2@hp.com>]

On Fri, 2015-03-27 at 10:03 +0530, Preeti U Murthy wrote:
> Hi Wanpeng
> 
> On 03/27/2015 07:42 AM, Wanpeng Li wrote:
> > Hi Preeti,
> > On Thu, Mar 26, 2015 at 06:32:44PM +0530, Preeti U Murthy wrote:
> >>
> >> 1. An ILB CPU was chosen from the first numa domain to trigger nohz idle
> >> load balancing [Given the experiment, upto 6 CPUs per core could be
> >> potentially idle in this domain.]
> >>
> >> 2. However the ILB CPU would call load_balance() on itself before
> >> initiating nohz idle load balancing.
> >>
> >> 3. Given cores are SMT8, the ILB CPU had enough opportunities to pull
> >> tasks from its sibling cores to even out load.
> >>
> >> 4. Now that the ILB CPU was no longer idle, it would abort nohz idle
> >> load balancing
> > 
> > I don't see abort nohz idle load balancing when ILB CPU was no longer idle 
> > in nohz_idle_balance(), could you explain more in details?
> 
> When the ILB CPU pulls load in rebalance_domains(), its idle state
> is set to CPU_NOT_IDLE.
> 
> ""
> idle = idle_cpu(cpu) ? CPU_IDLE : CPU_NOT_IDLE;

Hi Preeti,

The "idle" variable is a local variable to the rebalance_domains()
function. In that case, that shouldn't have an affect on the idle value
that gets passed to nohz_idle_balance().