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Red Hat injects RHEL with new iron love

Yesterday's kernel, today's chips

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Red Hat has pushed out another rev of its Linux variant. With Enterprise Linux 5.5, support for the latest processors from Advanced Micro Devices, Intel, and IBM has been back-ported to the Linux 2.6.18 at the heart of the RHEL 5 stack.

According to Tm Burke, vice president of platform engineering at Red Hat, the kernel in RHEL 5.5 has been improved, and it now includes features from more current Linux kernels, so it's not particularly fair to call it Linux 2.6.18. The point is that any application that was certified to run on Linux 2.6.18 or later, possibly many years ago, will work on RHEL 5.5 and still have support for new hardware like the Power7 processors from IBM that debuted back in February, the "Westmere-EP" Xeon 5600s from Intel that came out two weeks ago, the "Magny-Cours" Opteron 6100s from AMD that launched earlier this week, and the "Nehalem-EX" Xeon 7500s that were announced yesterday.

Because machines based on the Opteron 6100s, Xeon 7500, and Power7 processors all use a form of non-uniform memory access (NUMA) memory sharing across multiple processor sockets and also have multiple cores and caches inside sockets, RHEL 5.5 includes a lot of work that makes the operating system very aware of the system topology so memory allocation and job scheduling is done such that instruction streams and their data are placed as close together as possible. The kernel also has tweaks that try to cram as much work on as few cores as possible, allowing for servers to conserve power as they dial down or quiesce cores in the systems.

The updated RHEL also has a lot of I/O optimizations to take advantage of virtual I/O hardware features in the most current x64 and Power processors, which cuts down on I/O overhead in virtualized environments. In I/O-heavy virtualized workloads where the I/O was virtualized in software, rather than on the chip, the I/O overhead could be as high as 30 per cent, which is unacceptable.

Burke says that with these tweaks for I/O virtualization, which include a feature called Single Root I/O Virtualization (SR-IOV), a guest operating system running inside either a Xen or KVM hypervisor embedded in RHEL 5.5 can drive a 10 Gigabit Ethernet adapter card to its saturation point, and Burke claims this is the only hypervisor environment today that can do this. (That won't last for long, with RHEL being open source).

While the freestanding KVM hypervisor at the heart of the Red Hat Enterprise Virtualization, or RHEV, product was updated with a beta of its own 2.2 release using the RHEL 5.5 kernel earlier this week, RHEL 5.5 is available today and supports fatter guest virtual machines. The RHEV 2.2 beta can support 16 virtual CPUs and up to 256 GB of memory per guest, but RHEL 5.5 can support 32 physical processor cores and up to 512 GB of memory on either a Xen or KVM guest.

The bare-metal RHEL 5.5 kernel can support up to 1 TB of physical memory and can support well beyond the current top-end 64 sockets delivered today in eight-way Xeon 7500 systems. The open source community has already figured out how to do 512-core NUMA systems for the Itanium chips and is leveraging this work as x64 architectures get fatter. The RHEL 5 kernel has a stunning theoretical maximum of 32,000 threads that it can support, which is well beyond anything any server maker can put into the field in a single system image. Later this year, IBM's top-end Power 795 systems will have 32 sockets with a total of 256 cores and 1,024 threads.

The largest general-purpose Xeon 7500 machines will have maybe 64-sockets, which means 512 cores and 1,024 threads, and it looks like Itanium 9300 machines will probably top out at 64 sockets as well, but those quad-core chips only have eight threads, so that's a maximum of 512 threads. AMD is topped out at 40 threads in four-socket boxes with the Opteron 6100s. That will barely tickle the limits of RHEL 5.5.

By the way, RHEL 4 is not getting support for all this new iron, since Red Hat stopped doing major backporting to this early RHEL version six months ago. At some point, says Burke, the changes that would be necessary make new hardware work on the older versions without breaking application compatibility would involve way too much work or not be possible at all.

In general, a RHEL version gets three years of cutting-edge hardware support (roughly updated every six months), one year of transitional support where major hardware enablement and driver work is done, but perhaps not the greatest amount of tuning, and then three years where the version is in maintenance mode, with bug fixes and security patches. The expectation is that RHEL 5 will have a couple more years of hardware maintenance, but it really depends on how radical the hardware changes are in the future. If the changes are too radical, RHEL 5 gets sent to pasture sooner.

In addition to the updated hardware support, RHEL 5.5 has pulled in OpenOffice 3.1, which has better compatibility with Microsoft's Office 2007 formats, and the Samba print and file server has been updated to work with Windows 7. The SystemTap dynamic tracing tool that is part of the development stack in RHEL has also been enhanced so it can probe and poke C++ applications, rather than just C apps. The GDB debugger also has better support for C++ applications in that it allows developers to debug one thread at a time instead of having to suspend all threads in C++ code at the same time.

RHEL 5.5 also includes the full set of bug fixes and security patches since RHEL 5.4 came out last September. ®

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