Red Hat Continues Feature Expansion with RHEL 5.2

Published: May 21, 2008

by Timothy Prickett Morgan

As is traditional with Enterprise Linux releases from Red Hat, the latest RHEL 5.2 update that begins shipping today has a bunch of patches to make it work better on recently announced processors and related I/O peripherals. The update, which went into beta in March, also has the usual refresh of the open source stack for Linux as well as bug fixes and security patches. Significantly, the updated Linux kernel also includes support for more scalable processor clusters, for both physical machines and virtual machines.

As previously reported in The Linux Beacon, RHEL 5.2 is based on a recent iteration of the Linux 2.6.18 kernel, which was the heart of the original RHEL 5.0 operating system launched in March 2007, but that kernel has been updated by Red Hat engineers to support features that are in the current Linux 2.6.24 kernel. A lot of the enhancements have to do with virtualization, as you might expect, and rather than adopt the new kernel as-is, which would require customers to go through a new test and certification cycle, Red Hat instead keeps application binary interface (ABI) and application programming interface (API) compatibility by moving new features backward into the earlier Linux kernel. This is a successful tactic that Red Hat has done since the launch of Linux Advanced Server, which had the Linux 2.2 kernel with a bunch of Linux 2.4 features still in development then hardened and moved backwards by Red Hat, giving the company a big jump on the competition.

One of the most important things about RHEL 5.2 is that it supports much more scalable servers and larger main memories. As Red Hat said back in the beta program, RHEL 5.2 supports physical servers with up to 64 processor cores and with as much as 512 GB of main memory. But according to Daniel Riek, product marketing manager for Enterprise Linux at Red Hat, this scalability also applies to virtual machine images that make use of the integrated Xen 3.1.2 hypervisor in the box. (Presumably, that means a Xen partition can span up to 64 cores, but it is not clear from the release notes. I have a hard time believing that Xen can span more than eight or 16 cores in a virtual image.) RHEL 5.1 supported 32 processors in terms of maximum scalability, and may have topped out at 16 cores in terms of practical use. So this is a big jump in scalability. The fact that the Xen hypervisor can also see and support NUMA-style clustering is also important for Xeon based machines with more than four sockets and for any Opteron-based machines with more than a single socket if they use the glueless NUMA capability of the Opteron processor. Up until now, the Xen hypervisor could not see NUMA clustering, which means on a NUMA machine, a virtual machine tapped out at a single socket's worth of CPU cores.

Interestingly, the bare-metal Linux kernel inside RHEL, like other Linuxes, tops out at 256 logical processor cores, and this is a limit imposed not by the kernel, but by the Advanced Programmable Interrupt Controller (APIC) architecture that Intel created in the early 1990s for its first symmetric multiprocessing (SMP) servers. The APIC architecture is what allowed Intel to glue together two and then four Pentium processors into a single image for the operating system to play on.

RHEL 5.2 also now supports frequency scaling within virtual machines, a feature that has been in the bare-metal Linux kernel inside RHEL 5 for a while. Now, virtual machines can reach back through Xen and tell processor cores on which they are running to either increase or decrease the clock speeds of those cores depending on the workload needs inside the virtual machines. According to Riek, the virtualized support of frequency scaling only works on the most recent processors available from Intel and Advanced Micro Devices. Think any "Woodcrest" or later Core architecture Xeon and any Rev F or later Opteron. It is not clear if RHEL 5.2 hooks into similar frequency scaling features on IBM's Power6 and Intel's Itanium 9000 processors. Presumably it does, and presumably IBM and Red Hat have worked to get support for the Power6 chip's decimal math units and AltiVec vector processors into the RHEL 5.2 update. But maybe not. (I am trying to track this down as I write.)

Red Hat is officially supporting the latest Cell Power microprocessors, developed by IBM, Sony, and Toshiba for game consoles, electronics, and graphics processing, with RHEL 5.2, too. The future "Nehalem" octocore Xeon and current "Barcelona" quad-core Opteron processors were supported way back in RHEL 4.6, so customers with RHEL 4 do not need to move to the new RHEL 5.X version to get hardware support for these future chips and their servers.

Red Hat is planning on putting out RHEL 4.7 on July 21, which will include updates for hardware, bug fixes, and security patches. It RHEL 4.7 goes into beta testing this week. Riek says that Red Hat is going to get RHEL 5.3 out the door in January or so, which is a bit later than you might expect but which is possible because vendors are not updating hardware at a feverish pace and which is desirable because Red Hat wants to better align RHEL with its Fedora development Linux.

Just in case you didn't realize this (I certainly didn't until recently), Red Hat is the only commercial Linux distributor that is supporting the Xen hypervisor on Itanium processors, which was previewed back with RHEL 5.0 more than a year ago and which was officially supported with RHEL 5.1 in November 2007. In general, according to Riek, the Itanium variant of Xen will lag the X64 variant by about six months, which means it will be one release behind.

With the 5.2 update, Red Hat is also refreshing the stack of productivity software for end users in its Enterprise Linux 5.2 Desktop spin, including OpenOffice 2.3 and Firefox 3. The company has also updated graphics drivers and did a lot of work on the suspend/resume functions of laptops, which are cranky on all operating systems--Linux being no exception.

Customers who have subscriptions for either server or desktop variants of Red Hat Linux can get the 5.2 updates for free, as usual.

In a related announcement, Red Hat last week announced that paravirtualized I/O drivers have been added to RHEL 3, which allows RHEL 3 guests to run at near native speed atop the Xen hypervisor inside RHEL 5. (Because of paravirtualization, RHEL 3 doesn't really know it doesn't own a piece of hardware and doesn't realize it is virtualized at all.) RHEL 4.5 included a paravirtualized kernel, which means that RHEL 4.5 and higher instances can already be consolidated onto Xen hypervisors inside RHEL 5.

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