PiBooster: Performance Accelerations in Page Table Management for Paravirtual VMs

Abstract

In paravirtualization, the page table management components of the guest operating systems are properly patched for the security guarantees of the hypervisor. However, none of them pay enough attentions to the performance improvements, which results in two noticeable performance issues. First, such security patches exacerbate the problem that the execution paths of the guest page table (de)allocations become extremely long, which would consequently increase the latencies of process creations and exits. Second, the patches introduce many additional IOTLB flushes, leading to extra IOTLB misses, and the misses would have negative impacts on I/O performance of all peripheral devices. In this paper, we propose PiBooster, a novel lightweight approach for improving the performance in page table management. First, PiBooster shortens the execution paths of the page table (de)allocations by the PiBooster cache, which maintains dedicated buffers for serving page table (de)allocations. Second, PiBooster eliminates the additional IOTLB misses with a fine-grained validation scheme, which performs page table and DMA validations separately, instead of doing both together. We implement a prototype on Xen with Linux as the guest kernel. We do small modifications on Xen (166 SLoC) and Linux kernel (350 SLoC). We evaluate the I/O performance in both micro and macro ways. The micro experiment results indicate that PiBooster is able to completely eliminate the additional IOTLB flushes in the workload-stable environments, and effectively reduces (de)allocation time of the page table by 47% on average. The macro benchmarks show that the latencies of the process creations and exits are expectedly reduced by 16% on average. Moreover, the SPECINT,lmbench and netperf results indicate that PiBooster has no negative performance impacts on CPU computation, network I/O, and disk I/O.