On Fri, Apr 25, 2014 at 10:00:02AM +0200, Vincent Guittot wrote: > On 24 April 2014 21:30, Yuyang Du <yuyang...@intel.com> wrote: > > Hi Ingo, PeterZ, and others, > > > > The current scheduler's load balancing is completely work-conserving. In > > some > > workload, generally low CPU utilization but immersed with CPU bursts of > > transient tasks, migrating task to engage all available CPUs for > > work-conserving can lead to significant overhead: cache locality loss, > > idle/active HW state transitional latency and power, shallower idle state, > > etc, which are both power and performance inefficient especially for today's > > low power processors in mobile. > > > > This RFC introduces a sense of idleness-conserving into work-conserving (by > > all means, we really don't want to be overwhelming in only one way). But to > > what extent the idleness-conserving should be, bearing in mind that we don't > > want to sacrifice performance? We first need a load/idleness indicator to > > that > > end. > > > > Thanks to CFS's "model an ideal, precise multi-tasking CPU", tasks can be > > seen > > as concurrently running (the tasks in the runqueue). So it is natural to use > > task concurrency as load indicator. Having said that, we do two things: > > > > 1) Divide continuous time into periods of time, and average task > > concurrency > > in period, for tolerating the transient bursts: > > a = sum(concurrency * time) / period > > 2) Exponentially decay past periods, and synthesize them all, for > > hysteresis > > to load drops or resilience to load rises (let f be decaying factor, and a_x > > the xth period average since period 0): > > s = a_n + f^1 * a_n-1 + f^2 * a_n-2 +, .....,+ f^(n-1) * a_1 + f^n * a_0 > > In the original version of entity load tracking patchset, there was a > usage_avg_sum field that was counting the time the task was really > running on the CPU. By combining this (disappeared ) field with the > runnable_avg_sum, you should have similar concurrency value but with > the current load tracking mechanism (instead of creating new one).
I'm not entire sure understood what was proposed, but I suspect its very close to what I told you to do with the capacity muck. Use avg utilization instead of 1 active task per core. And yes, the current load tracking should be pretty close. We just need to come up another way of doing SMT again, bloody inconvenient SMT. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
