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118 • Linux Symposium 2004 • Volume One page of memory where its receive queue resides, and a partition wishing to send a message to its partner’s queue issues an h_send_crq hypervisor call. When a message is received on the queue, an interrupt is (optionally) generated in the receiving partition. The second hypervisor mechanism is a facility for issuing DMA operations between partitions. The h_copy_rdma call is used to DMA a block of memory from the memory space of one logical partition to the memory space of another. The virtual SCSI interpartition protocol is implemented using the ANSI “SCSI RDMA Protocol” (SRP) (available at http://www. t10.org). When the client wishes to issue a SCSI operation, it builds an SRP frame, and sends the address of the frame in a 16 byte CRQ message. The server DMA’s the SRP frame from the client, and processes it. The SRP frame may itself contain DMA addresses required for data transfer (read or write buffers, for example) which may require additional interpartition DMA operations. When the operation is complete, the server DMA’s the SRP response back to the same location as the SRP command came from and sends a 16 byte CRQ message back indicating that the SCSI command has completed. The current Linux virtual SCSI server decodes incoming SCSI commands and issues block layer commands (generic_make_ request). This allows the SCSI server to share any block device (e.g., /dev/sdb6 or /dev/loop0) with client partitions as a virtual SCSI device. Note that consideration was given to using protocols such as iSCSI for device sharing between partitions. The virtual SCSI SRP design above, however, is a much simpler design that does not rely on riding above an existing IP stack. Additionally, the ability to use DMA operations between partitions fits much better into the SRP model than an iSCSI model. The Linux virtual SCSI client (drivers/ scsi/ibmvscsi/ibmvscsi.c) is close, at the time of writing, to being accepted into the Linux mainline. The Linux virtual SCSI server is sufficiently unlike existing SCSI drivers that it will require much more mailing list “discussion.” 4.4 Virtual TTY In addition to virtual Ethernet and SCSI adapters, the hypervisor supports virtual serial (TTY) adapters. As with SCSI adapter, these can be configured as “client” adapters, and “server” adapters and connected between partitions. The first virtual TTY adapter is used as the system console, and is treated specially by the hypervisor. It is automatically connected to the partition console on the Hardware Management Console. To date, multiple concurrent “consoles” have not been implemented, but they could be. Similarly, this interface could be used for kernel debugging as with any serial port, but such an implementation has not been done. 5 Dynamic Resource Movement As mentioned for processors, the logical partition environment lends itself to moving resources (processors, memory, I/O) between partitions. In a perfect world, such movement should be done dynamically while the operating system is running. Dynamic movement of processors is currently being implemented, and dynamic movement of I/O devices (including dynamically adding and removing virtual I/O devices) is included in the kernel mainline. The one area for future work in Linux is the dynamic movement of memory into and out of an
Linux Symposium 2004 • Volume One • 119 active partition. This function is already supported on other POWER5 operating systems, so there is an opportunity for Linux to catch up. 6 Multiple Operating Systems A key feature of the POWER5 systems is the ability to run different operating systems in different logical partitions on the same physical system. The operating systems currently supported on the POWER5 hardware are AIX, OS/400, and Linux. While running multiple operating systems, all of the functions for interpartion interaction described above must work between operating systems. For example, idle cycles from an AIX partition can be given to Linux. A processor can be moved from OS/400 to Linux while both operating systems are active. For I/O, multiple operating systems must be able to communicate over the virtual Ethernet, and SCSI devices must be sharable from (say) an AIX virtual SCSI server to a Linux virtual SCSI client. These requirements, along with the architected hypervisor interfaces, limit the ability to change implementations just to fit a Linux kernel internal behavior. 7 Conclusions While many of the basic virtualization technologies described in this paper existed in the Linux implementation provided on POWER RS64 and POWER4 iSeries systems [Bou01], they have been significantly enhanced for POWER5 to better use the firmware provided interfaces. The introduction of POWER5-based systems converged all of the virtualization interfaces provided by firmware on legacy iSeries and pSeries systems to a model in line with the legacy pSeries partitioned system architecture. As a result much of the PPC64 Linux virtualization code was updated to use these new virtualization interface definitions. 8 Acknowledgments The authors would like to thank the entire Linux/PPC64 team for the work that went into the POWER5 virtualization effort. In particular Anton Blanchard, Paul Mackerras, Rusty Rusell, Hollis Blanchard, Santiago Leon, Ryan Arnold, Will Schmidt, Colin Devilbiss, Kyle Lucke, Mike Corrigan, Jeff Scheel, and David Larson. 9 Legal Statement This paper represents the view of the authors, and does not necessarily represent the view of IBM. IBM, AIX, iSeries, OS/400, POWER, POWER4, POWER5, and pSeries are trademarks or registered trademarks of International Business Machines Corporation in the United States, other countries, or both. Other company, product or service names may be trademerks or service marks of others. References [AAN00] Bill Armstrong, Troy Armstrong, Naresh Nayar, Ron Peterson, Tom Sand, and Jeff Scheel. Logical Partitioning, http://www-1.ibm.com/servers/ eserver/iseries/beyondtech/ lpar.htm.
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Proceedings of the Linux Symposium
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