Intel Keeps Pushing Haswell Code For Linux

Intel continues to push out more open-source kernel code for enabling their next-generation Haswell processors to be properly supported under Linux.

Haswell, the successor to Intel's Ivy Bridge processors, isn't due to be released for a number of months still but Intel Open-Source Technology Center developers have already been working on Haswell Linux enablement for a number of months.

Since March we have been seeing Linux graphics driver code for Haswell that continues to be refined. Haswell (along with Valley View, the next-generation Atom SoC) continues to be extensively developed by the graphics team within Intel OTC and with the Linux 3.8 kernel the Haswell DRM driver should be in shape. There's many variants to Haswell's graphics cores.

Aside from enabling support for the next-generation Intel HD integrated graphics on Haswell CPUs, Intel Linux developers have also been working to enable other areas of their next-generation hardware on the open-source operating system. One of the other areas I've written about already has been the Haswell audio improvements for Linux.

There's also been compiler optimizations for Intel Haswell within GCC and LLVM in preparation for the new instruction set extensions to be added to the Haswell processors. One of the new compiler features for Haswell is AVX2. More of these additions, which are exposed via the "core-avx2" compiler micro-architecture flag, include FMA, BMI1, BMI2, and LZCNT instruction set extensions.

In recent days there have also been new Haswell patches to see the public spotlight on the Linux kernel mailing list. One of the new patch series to appear for Haswell on the mailing list is for LBR (Last Branch Record) call stack support. "Haswell has a new feature that utilizes the existing Last Branch Record facility to record call chains. When the feature is enabled, function call will be collected as normal, but as return instructions are executed the last captured branch record is popped from the on-chip LBR registers. The LBR call stack facility can help perf to get call chains of progam without frame pointer." This LBR call stack patch series in its current form can be seen here.

Another new patch series is perf PMU support for Haswell, which is now up to its third revision. "This adds perf PMU support for the upcoming Haswell core. The patchkit is fairly large, mainly due to various enhancement for TSX. TSX tuning relies heavily on the PMU, so I tried hard to make all facilities easily available. In addition it also has some other enhancements."

The latest round of Intel Haswell improvements for Linux should be merged for the next kernel cycle, the Linux 3.8 kernel. It's looking like Linux 3.8 is where everything should come together for decent Haswell CPU support under Linux, which will be making it into Ubuntu 13.04 and other Q2'2013 Linux distributions.

New features to be found with Haswell beyond AVX / FMA 3 / Haswell New Instructions will be new CPU sockets, Transactional Synchronization Extensions (TSX), significant graphics improvements, DDR4 in the enterprise/server space, a Variable Base Clock, and SMAP security support.