If commercial Unix vendors weren’t already worried about Linux, they should be now. Linux has seen wide deployment in datacenters, generally as a Web server or a file server, or to handle network tasks such as DNS and DHCP, but not as a platform for running mission-critical enterprise applications. Solaris, AIX, or HP/UX typically get the nod when an application demands the highest levels of performance and scalability. The recent release of a new Linux kernel, v2.6, promises to change that.
The v2.6 kernel ushers in a new era of support for big iron with big workloads, opening the door for Linux to handle the most demanding tasks that are currently handled by Solaris, AIX, or HP/UX. The new kernel not only supports greater amounts of RAM and a higher processor count, but the core of device management has changed. Previous to this kernel there were limits within the kernel that could constrain large systems, such as a 65,536 process limit before rollover, and 256 devices per chain. The v2.6 kernel moves well beyond these limitations, and it includes support for some of the largest server architectures around.
Will the new Linux really perform in the same league as the big boys? To find out, I put the v2.6.0 kernel through several real-world performance tests, comparing its file server, database server, and Web server performance with a recent v2.4 series kernel, v2.4.23.
Linux Meets Big Iron
A primary focus of the v2.6 kernel is large server architectures. Support for up to 64GB RAM in paged mode, the ability to address file systems larger than 2TB, and support for 64 CPUs in x86-based SMP systems brings this kernel and Linux into the more rarified air of truly mission-critical systems. The included support for NUMA (Non-Uniform Memory Access) systems; a next-generation SMP architecture; and PAE (Physical Address Extensions), providing support for up to 64GB of RAM on 32-bit systems, is also new.
There is much more to v2.6 than just bigger numbers in processor and RAM counts, however. This kernel breaks apart some of the artificial limitations that have been present in Linux from the beginning, such as the number of addressable devices and total available PIDs (Processor Identifiers). The v2.4 kernel supported 255 major devices with 255 minor numbers. (For example, a volume on a SCSI disk located at /dev/sda3 has a major number of 8, since it’s a SCSI device, and a minor number of 3.) On servers with a large number of real or virtual devices, device allocation can become problematic. The v2.6 kernel addresses these issues in a big way, moving to 4,096 major devices with more than one million subdevices per major device. For most users, these numbers are well beyond practical limits, but for enterprise systems with a need to address many devices, it’s a major step.
Also new in v2.6 is NPTL (Native POSIX Threading Library) in lieu of v2.4’s LinuxThreads. NPTL brings enterprise-class threading support to Linux, far surpassing the performance offered by LinuxThreads. As of October 2003, NPTL support was merged into the GNU C library, glibc, and Red Hat first implemented NPTL within Red Hat Linux 9 using a customized v2.4 kernel.