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Redesigning Xen's Memory Sharing Mechanism for Safe and Efficient I/O Virtualization

Ram, Kaushik Kumar; Santos, Jose Renato; Turner, Yoshio
HP Laboratories


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Abstract: Xen's memory sharing mechanism, called the grant mechanism, is used to share I/O buffers in guest domains' memory with a driver domain. Previous studies have identified the grant mechanism as a significant source of network I/O overhead in Xen. This paper describes a redesigned grant mechanism to significantly reduce the associated overheads. Unlike the original grant mechanism, the new mechanism allows guest domains to unilaterally issue and revoke grants. As a result, the new mechanism makes it simple for the guest OS to reduce the number of grant issue and revoke operations that are needed for I/O by taking advantage of temporal and/or spatial locality in its use of I/O buffers. Another benefit of the new mechanism is that it provides a unified interface for memory sharing, whether between guest and driver domains, or between guest domains and I/O devices using IOMMU hardware. We have developed an implementation of the new grant mechanism that fully supports driver domains, but not yet IOMMUs. The paper presents performance results using this implementation which show that the new mechanism reduces per-packet overhead by up to 31% and increases network throughput by up to 52%.

8 Pages

Additional Publication Information: Published and presented at the Second Workshop on I/O Virtualization (WIOV '10), March 13, 2010, Pittsburgh, PA, USA.

External Posting Date: March 21, 2010 [Fulltext]. Approved for External Publication
Internal Posting Date: March 21, 2010 [Fulltext]

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