Compiling for niceness: mitigating contention for QoS in warehouse scale computers

As the class of datacenters recently coined as warehouse scale computers (WSCs) continues to leverage commodity multicore processors with increasing core counts, there is a growing need to consolidate various workloads on these machines to fully utilize their computation power. However, it is well known that when multiple applications are co-located on a multicore machine, contention for shared memory resources can cause severe cross-core performance interference. To ensure that the quality of service (QoS) of user-facing applications does not suffer from performance interference, WSC operators resort to disallowing co-location of latency-sensitive applications with other applications. This policy translates to low machine utilization and millions of dollars wasted in WSCs. This paper presents QoS-Compile, the first compilation approach that statically manipulates application contentiousness to enable the co-location of applications with varying QoS requirements, and as a result, can greatly improve machine utilization. Our technique first pinpoints an application's code regions that tend to cause contention and performance interference. QoS-Compile then transforms those regions to reduce their contentious nature. In essence, to co-locate applications of different QoS priorities, our compilation technique uses pessimizing transformations to throttle down the memory access rate of the contentious regions in low priority applications to reduce their interference to high priority applications. Our evaluation using synthetic benchmarks, SPEC benchmarks and large-scale Google applications show that QoS-Compile can greatly reduce contention, improve QoS of applications, and improve machine utilization. Our experiments show that our technique improves applications' QoS performance by 21% and machine utilization by 36% on average.