With the ever-growing need of data in HPC applications, the congestion at the I O level becomes critical in super-computers. Architectural enhancement such as burst-buffers and pre-fetching are added to machines, but are not sufficient to prevent congestion. Recent online I O scheduling strategies have been put in place, but they add an additional congestion point and overheads in the computation of applications. In this work, we show how to take advantage of the periodic nature of HPC applications in order to develop efficient periodic scheduling strategies for their I O transfers. Our strategy computes once during the job scheduling phase a pattern where it defines the I O behavior for each application, after which the applications run independently, transferring their I O at the specified times. Our strategy limits the amount of I O congestion at the I O node level and can be easily integrated into current job schedulers. We validate this model through extensive simulations and experiments by comparing it to state-of-the-art online solutions, showing that not only our scheduler has the advantage of being de-centralized and thus overcoming the overhead of online schedulers, but also that it performs better than these solutions, improving the application dilation up to 13 and the maximum system efficiency up to 18 .
The study from @cite_8 offers ways of isolating the performance experienced by applications of one operating system from variations in the I O request stream characteristics of applications of other operating systems. While their solution cannot be applied to HPC systems, the study offers a way of controlling the coarse grain allocation of disk time to the different operating system instances as well as determining the fine-grain interleaving of requests from the corresponding operating systems to the storage system.
@cite_8
1988404188 1572047826 2150864656 2018997957
Unmatched computation and storage performance in new HPC systems have led to a plethora of I O optimizations ranging from application-side collective I O to network and disk-level request scheduling on the file system side. As we deal with ever larger machines, the interferences produced by multiple applications accessing a shared parallel file system in a concurrent manner become a major problem. These interferences often break single-application I O optimizations, dramatically degrading application I O performance and, as a result, lowering machine wide efficiency. This paper focuses on CALCioM, a framework that aims to mitigate I O interference through the dynamic selection of appropriate scheduling policies. CALCioM allows several applications running on a supercomputer to communicate and coordinate their I O strategy in order to avoid interfering with one another. In this work, we examine four I O strategies that can be accommodated in this framework: serializing, interrupting, interfering and coordinating. Experiments on Argonne's BG P Surveyor machine and on several clusters of the French Grid'5000 show how CALCioM can be used to efficiently and transparently improve the scheduling strategy between two otherwise interfering applications, given specified metrics of machine wide efficiency. A significant percentage of the computing capacity of large-scale platforms is wasted because of interferences incurred by multiple applications that access a shared parallel file system concurrently. One solution to handling I O bursts enlarge-scale HPC systems is to absorb them at an intermediate storage layer consisting of burst buffers. However, our analysis of the Argonne's Mira system shows that burst buffers cannot prevent congestion at all times. Consequently, I O performances dramatically degraded, showing in some cases a decrease in I O throughput of 67 . In this paper, we analyze the effects of interference on application I O bandwidth and propose several scheduling techniques to mitigate congestion. We show through extensive experiments that our global I O scheduler is able to reduce the effects of congestion, even on systems where burst buffers are used, and can increase the overall system throughput up to 56 . We also show that it outperforms current Mira I O schedulers. The underutilization of disk parallelism and file cache buffers by traditional file systems induces I O stall time that degrades the performance of modern microprocessor-based systems. In this paper, we present aggressive mechanisms that tailor file system resource management to the needs of I O-intensive applications. In particular, we show how to use application-disclosed access patterns (hints) to expose and exploit I O parallelism and to allocate dynamically file buffers among three competing demands: prefetching hinted blocks, caching hinted blocks for reuse, and caching recently used data for unhinted accesses. Our approach estimates the impact of alternative buffer allocations on application execution time and applies a cost-benefit analysis to allocate buffers where they will have the greatest impact. We implemented informed prefetching and caching in DEC''s OSF 1 operating system and measured its performance on a 150 MHz Alpha equipped with 15 disks running a range of applications including text search, 3D scientific visualization, relational database queries, speech recognition, and computational chemistry. Informed prefetching reduces the execution time of the first four of these applications by 20 to 87 . Informed caching reduces the execution time of the fifth application by up to 30 . Virtualized storage systems are required to service concurrently executing workloads, with potentially diverse data delivery requirements, that are running under multiple operating systems. Although a number of algorithms have been developed for I O performance virtualization among operating system (OS) instances and their applications, none results in absolute performance virtualization. By absolute performance virtualization we mean that the performance experienced by applications of one operating system does not suffer due to variations in the I O request stream characteristics of applications of other operating systems. Key requirements of I O performance virtualization are fairness and performance isolation. In this paper, we present a novel virtual I O scheduler (VIOS) that provides absolute performance virtualization by being fair in sharing I O system resources among operating systems and their applications, and provides performance isolation in the face of variations in the characteristics of I O streams. The VIOS controls the coarse grain allocation of disk time to the different operating system instances and is OS independent; optionally, a set of OS-dependent schedulers may determine the fine-grain interleaving of requests from the corresponding operating systems to the storage system.