Yes, I am interested.


-----Original Message-----
From: Muli Ben-Yehuda [mailto:[EMAIL PROTECTED] 
Sent: Thursday, April 05, 2007 6:46 PM
Subject: [Haifux] another lecture proposal

If there's interest, I'll be happy to give this talk I'll be giving at OLS
'07 at Haifux as well.

The Price of Safety: Evaluating IOMMU Performance

IOMMUs, "IO Memory Management Units", are hardware devices that translate
device DMA addresses to machine addresses. Isolation capable IOMMUs perform
a valuable system service, preventing rogue devices from performing errant
or malicious DMAs, thereby substantially increasing the system's reliability
and availability. Without an IOMMU, a peripheral device could be programmed
to overwrite any part of the system's memory. An isolation capable IOMMU
restricts a device so that it can only access parts of memory it has been
explicitly granted access to. Operating systems utilize IOMMUs to isolate
device drivers; hypervisors utilize IOMMUs to grant secure direct hardware
access to virtual machines. With the imminent publication of the PCI-SIG's
IO Virtualization standard, as well as Intel and AMD's introduction of
isolation capable IOMMUs in all new servers, IOMMUs will become ubiquitous.

IOMMUs can impose a performance penalty due to the extra memory accesses
required to perform DMA operations. The exact performance degradation
depends on the IOMMU design, its caching architecture, the way it is
programmed and the workload. In this paper, we present the performance
characteristics of the Calgary and DART IOMMUs in Linux, both on bare metal
and hypervisors. We measure the throughput and CPU utilization of several IO
workloads with and without an IOMMU and analyze the results. We then discuss
potential strategies for mitigating the IOMMU's costs. We conclude by
presenting a set of optimizations we have implemented and the resulting
performance improvements.


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