Don’t Forget the I/O When Allocating Your LLC
Don’t Forget the I/O When Allocating Your LLC
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DOI：
10.1109/isca52012.2021.00018
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发表时间：
2021-06
期刊：
影响因子：
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通讯作者：
Yifan Yuan;Mohammad Alian;Yipeng Wang;Ren Wang;I. Kurakin;Charlie Tai;N. Kim
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文献类型：
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作者：
Yifan Yuan;Mohammad Alian;Yipeng Wang;Ren Wang;I. Kurakin;Charlie Tai;N. Kim
在现代服务器CPU中，末级缓存（LLC）是影响工作负载性能的关键硬件资源，如何管理LLC是多租户云环境下性能隔离和QoS的关键。在本文中，我们认为，除了CPU核心，高速I/O也是LLC管理的重要。这是因为英特尔架构创新-数据直接I/O（DDIO）-直接将入站I/O流量注入LLC（部分），而不是主内存。本文总结了DDIO带来的两个问题：（1）默认的DDIO配置并不总是能获得最佳性能;（2）DDIO会使与其共享LLC的非I/O工作负载的性能下降高达32%;并提出了第一种将I/O视为一等公民的LLC管理机制。Iat使用CPU的硬件性能计数器监视和分析核心/LLC/DDIO的性能，并自适应地调整用于DDIO或需要更多LLC容量的租户的LLC路的数量。此外，Iat动态地选择与DDIO共享其LLC资源的租户，以最小化租户和I/O的性能干扰。我们的实验与多个微基准和现实世界的应用程序表明，以最小的开销，Iat可以有效地和稳定地减少DDIO造成的性能下降。
In modern server CPUs, last-level cache (LLC) is a critical hardware resource that exerts significant influence on the performance of the workloads, and how to manage LLC is a key to the performance isolation and QoS in the cloud with multi-tenancy. In this paper, we argue that in addition to CPU cores, high-speed I/O is also important for LLC management. This is because of an Intel architectural innovation – Data Direct I/O (DDIO) – that directly injects the inbound I/O traffic to (part of) the LLC instead of the main memory. We summarize two problems caused by DDIO and show that (1) the default DDIO configuration may not always achieve optimal performance, (2) DDIO can decrease the performance of non-I/O workloads that share LLC with it by as high as 32%.We then present, the first LLC management mechanism that treats the I/O as the first-class citizen. Iat monitors and analyzes the performance of the core/LLC/DDIO using CPU’s hardware performance counters and adaptively adjusts the number of LLC ways for DDIO or the tenants that demand more LLC capacity. In addition, Iat dynamically chooses the tenants that share its LLC resource with DDIO to minimize the performance interference by both the tenants and the I/O. Our experiments with multiple microbenchmarks and real-world applications demonstrate that with minimal overhead, Iat can effectively and stably reduce the performance degradation caused by DDIO.