1. Resource Aware Scheduler – Initial Results
Tomer Morad, Noam Shalev,
Avinoam Kolodny, Idit Keidar, Uri Weiser
May 8, 2013

2. Main Message: Balance Systems to Avoid Bottlenecks
Motivation
Different programs have different resource requirements: # of cores, cache, memory bandwidth, energy, branch prediction, etc.
Hence, no computing system can be balanced
Heterogeneous systems are even worse (unbalanced)
Contention on resources wastes energy and usually degrades performance (for example: cache)
Proposal: dynamically tune the workload to the (dynamically tuned) hardware in order to minimize the contention on the resources by balancing the system
The OS scheduler can do this

3. CMP Shared Resource Effects
Examples for shared resources: last level cache, memory bus, network bandwidth, disk bandwidth, etc.
There are three effects observed when several threads access a shared resource
Wasted Peripheral Energy (⬆ Energy)
Observed when adding additional threads in a presence of a bottleneck
For example: many floating point programs running in parallel in a Niagara processor (many cores with a shared floating point unit)
Collisions (⬆ Energy, ⬇ Throughput)
Observed when several threads access a shared resources, and the requests are queued
In the example above, the service to the requests is slower
Destructive Interference (⬆ Energy, ⬇ Throughput)
Observed when threads destroy each others’ caches

4. Resource Aware OS scheduler
Main Components:
Sampling: Sample the resource usage of the tasks that have run so that the information will be available for the prediction stage
Prediction: Predict each task’s resource usage based on the past resource usage
Scheduling: Schedule only tasks that the system has enough resources to run (idle cores are OK)
Implemented in Linux 3.2.0
Use performance counters for sampling

5. Memory Bandwidth – An Example
Core count is increasing
Core frequency does not decrease
Pin count is not increasing
Chip bandwidth demand is increasing, but
Chip bandwidth to memory is not increasing
We are approaching the memory bandwidth wall!
No real remedies in the near future

6. Memory Bus Usage

7. SPEC-CPU2006 on the baseline scheduler
Instance
Instances
Instances
Instances

8. BW hungry program – Initial results
Implemented a resource aware scheduler in the Linux 3.2.0
BW hungry program
5.58 sec, 132 Joules
When run x4 times sequentially
22.3 sec, 526 Joules
When run x4 times in parallel (4 core i5-2500)
27.86 sec (+25%), 1368 Joules (+160%) – over sequential
Using the new scheduler with memory bandwidth limitation enforcement
23.71 sec (+6%), 569 Joules (+8%) – over sequential
Baseline scheduler Vs Resource Aware Scheduler
17.5% speedup, 58% energy reduction
Disclaimers: (a) Initial results; (b) energy sampled using performance counter (MSR_PKG_ENERGY_STATUS) that samples the power used by the package. Consistent results with Wattsup

9. SPEC-CPU2006 – Initial results
Each run included four instances of identical SPEC-CPU2006 benchmarks
Average: +3.3% throughput, -3.5% energy
Notable results:
429: +106% throughput, -43% energy
473: +3.3% throughput, -13% energy
Out of 25 benchmarks
16 consumed less energy (9 consumed more)
10 ran faster (11 slower)
Other results
Energy efficiency improved on average by 11%
15 benchmarks’ energy efficiency improved by 20% on average
10 benchmarks’ energy efficiency degraded by 3% on average
Soft limit for the bandwidth anticipated to improve the results