http://summit.ubuntu.com/lpc-2012/ Scheduler

Wednesday 09:50 - 10:35 PDT
Not Attending Target CPU selection && Sharing Sched Info
=== How to improve the selection of the target cpu in the timer and workqueue framework === It's sometime difficult to move a timer/hrtimer on a set of cpus in order to follow the load balance policy of the scheduler. We have some use cases where a timer, that is not specifically pinned to a particular cpu, stays on this cpu (or set of cpus) whereas all the tasks activity has moved on other ones. The timer/hrtimer frameworks currently call a scheduler function under some conditions but there is a limited number of use case where the timer will effectively migrate. The wokqueue framework doesn't have any link with the scheduler when it looks for a cpu on which it can run a work. The goal of this talk is to describe the potential issue and to discuss the possible solution. Topic Lead: Vincent Guittot Vincent Guittot is an embedded Linux engineer at ST-Ericsson. Since 2005, he has focused on mobile phone running Linux and Android. In 2010, he has joined the power management working group of Linaro. === Sharing information between scheduler and frameworks === The scheduler could take advantage of information from other frameworks, when it selects run queue for a task. These information are helpful not only for power consumption but also for performance by giving a mask of preferred CPUs. As an example, the wake up latency of a task is impacted by the C-states of the selected CPU. Choosing a CPU with a low C-state will reduce this latency. This talk will discuss the various inputs that could be shared with the scheduler Topic Lead: Vincent Guittot

Participants:
attending apm (Antti P Miettinen)
attending paulmck (Paul McKenney)
attending vincent-guittot (Vincent Guittot)

Tracks:
  • Scheduler
Nautilus 2
Wednesday 14:50 - 15:35 PDT
Not Attending big.LITTLE && Tegra30
=== Task placement for asymmetric cores === Traditional SMP scheduling is basically aiming for equal load distribution across all CPUs. To take full advantage of the big.LITTLE MP power/performance heterogeneity, task affinity is crucial. I have experimented with modifications to the Linux scheduler, which attempt to minimizing power consumption by selecting task affinity appropriately for each task. Topic Lead: Morten Rasmussen === Scheduling and the big.LITTLE Architecture === ARM's big.LITTLE architecture is an example of asymmetric multiprocessing where all CPUs are instruction-set compatible, but where different CPUs have very different performance and energy-efficiency characteristics. In the case of big.LITTLE, the big CPUs are Cortex-A15 CPUs with deep pipelines and numerous functional units, providing maximal performance. In contrast, the LITTLE CPUs are Cortex-A7 with short pipelines and few functional units, which optimizes for energy efficiency. Linaro is working on two methods of supporting big.LITTLE systems. One way to configure big.LITTLE systems is in an MP configuration, where both the big and LITTLE CPUs are present. Traditionally, most SMP operating systems have assumed that all CPUs are identical, but this is emphatically not the case for big.LITTLE. Therefore, changes for big.LITTLE are required. This talk will give an overview of the progress towards the goal of big.LITTLE support in the Linux plumbing. Topic Lead: Paul E. McKenney === cpuquiet: Dynamic CPU core management === NVIDIA Tegra30 has CPU clusters with different abilities. There is a fast cluster with 4 cortex A9 cores and a low power cluster with a single cortex A9 core. Only 1 of the clusters can be active at a time. This means the number of available cores for the kernel changes at runtime. Currently we use CPU hotplug to make cores unavailable so we can initiate a switch to the low power cluster. This has a number of problems such as long latencies in switching between the clusters. Therefor a new mechanism where CPUs would not be available but still not completely removed from the system, would be useful. CPUs in this quiet state would not be running any userspace or kernelspace code, until they are explicitly made available again. The kernel datastructures associated with each CPU would be preserved however so a transitions can be a low latency operations. The policy can be encapsulated in a governor, like the cpufreq and cpuidle governors we already have. Topic Lead: Peter De Schrijver Peter is an NVIDIA Tegra Linux kernel engineer, Debian developer, previously working on power management in maemo for Nokia.

Participants:
attending apm (Antti P Miettinen)
attending paulmck (Paul McKenney)
attending srwarren (Stephen Warren)
attending vincent-guittot (Vincent Guittot)

Tracks:
  • Scheduler
Nautilus 5
Wednesday 15:45 - 16:30 PDT
Not Attending big.LITTLE && Tegra30
=== Task placement for asymmetric cores === Traditional SMP scheduling is basically aiming for equal load distribution across all CPUs. To take full advantage of the big.LITTLE MP power/performance heterogeneity, task affinity is crucial. I have experimented with modifications to the Linux scheduler, which attempt to minimizing power consumption by selecting task affinity appropriately for each task. Topic Lead: Morten Rasmussen === Scheduling and the big.LITTLE Architecture === ARM's big.LITTLE architecture is an example of asymmetric multiprocessing where all CPUs are instruction-set compatible, but where different CPUs have very different performance and energy-efficiency characteristics. In the case of big.LITTLE, the big CPUs are Cortex-A15 CPUs with deep pipelines and numerous functional units, providing maximal performance. In contrast, the LITTLE CPUs are Cortex-A7 with short pipelines and few functional units, which optimizes for energy efficiency. Linaro is working on two methods of supporting big.LITTLE systems. One way to configure big.LITTLE systems is in an MP configuration, where both the big and LITTLE CPUs are present. Traditionally, most SMP operating systems have assumed that all CPUs are identical, but this is emphatically not the case for big.LITTLE. Therefore, changes for big.LITTLE are required. This talk will give an overview of the progress towards the goal of big.LITTLE support in the Linux plumbing. Topic Lead: Paul E. McKenney === cpuquiet: Dynamic CPU core management === NVIDIA Tegra30 has CPU clusters with different abilities. There is a fast cluster with 4 cortex A9 cores and a low power cluster with a single cortex A9 core. Only 1 of the clusters can be active at a time. This means the number of available cores for the kernel changes at runtime. Currently we use CPU hotplug to make cores unavailable so we can initiate a switch to the low power cluster. This has a number of problems such as long latencies in switching between the clusters. Therefor a new mechanism where CPUs would not be available but still not completely removed from the system, would be useful. CPUs in this quiet state would not be running any userspace or kernelspace code, until they are explicitly made available again. The kernel datastructures associated with each CPU would be preserved however so a transitions can be a low latency operations. The policy can be encapsulated in a governor, like the cpufreq and cpuidle governors we already have. Topic Lead: Peter De Schrijver Peter is an NVIDIA Tegra Linux kernel engineer, Debian developer, previously working on power management in maemo for Nokia.

Participants:
attending apm (Antti P Miettinen)
attending paulmck (Paul McKenney)
attending srwarren (Stephen Warren)
attending vincent-guittot (Vincent Guittot)

Tracks:
  • Scheduler
Nautilus 5
Friday 15:05 - 15:50 PDT
Not Attending Application of deadline scheduling for powersaving strategies
Power consumption is an important issue in the design of real-time embedded and general purpose systems. How to reduce power consumption, enabling longer lifetime for battery powered systems, is however still an open problem. A real-time scheduling algorithm based on the deadline concept (like SCHED_DEADLINE) can be utilized to provide power-aware scheduling strategies. In this talk I will first present work that has been done in the past on the subject. Then I will propose some simple ideas on how deadline scheduling could be effective in reducing power consumption. Topic Lead: Juri Lelli

Participants:
attending paulmck (Paul McKenney)
attending vincent-guittot (Vincent Guittot)

Tracks:
  • Scheduler
Nautilus 2

PLEASE NOTE The Linux Plumbers Conference 2012 schedule is still in a draft format and is subject to changes at any time.