Kernel Podcast for Feb 20th, 2017

UPDATE: Thanks to LWN for the mention. This podcast is in “alpha”. It will start to show up on iTunes and Google Play (which didn’t exist last time I did this thing!) stores within the next day or two. You can also subscribe (for the moment) by using this link:¬†kernel podcast audio rss feed. This podcast format will be tweaked, and the format/layout will very likely change a bit as I figure out what works, and what does not. Equipment just started to arrive at home (Zoom H4N Pro, condenser mics, etc.), a new content publishing platform needs to get built (I intend ultimately for listeners to help to create summaries by annotating threads as they happen). And yes, my former girlfriend will once again be reprising her role as author of another catchy intro jingle…soon ūüėČ

Audio: Kernel Podcast 20170220

Support for this podcast comes from Jon Masters, trying to bring back the Kernel Podcast since 2012.

In this week’s edition: Linus Torvalds announces Linux 4.10, Alan Tull updates his FPGA manager framework, and Intel’s latest 5-level paging patch series is posted for review. We will have this, and a summary of ongoing development in the first of the newly revived Linux Kernel Podcast.

Linux 4.10

Linus Torvalds announced the release of 4.10 final, noting that “it’s¬†been quiet since rc8, but we did end up fixing several small issues,¬†so the extra week was all good”. Linus added a (relatively rare)¬†additional “RC8” (Release Candidate 8) to this kernel cycle due to¬†the timing – many of us were attending the “Open Source Leadership¬†Summit” (OSLS, formerly “Linux Foundation Collaboration Summit”, or¬†“Collab”) over the past week. The 4.10 kernel contains about 13,000¬†commits, which used to seem large but somehow now…isn’t. has the usual summary of new features and fixes:¬†

With the announcement of 4.10 comes the opening of the merge window for¬†Linux 4.11 (the period of up to two weeks at the beginning of a development¬†cycle, during with new features and disruptive changes are “pulled” into¬†Linus’s kernel (git) tree). The 4.11 merge window begins today.

FPGA Manager Updates

Alan Tull posted a patch series implementing “FPGA Region¬†enhancements and fixes”, which “intends to enable expanding¬†the user of FPGA regions beyond device tree overlays”. Alan’s¬†FPGA manager framework allows the kernel to manage regions¬†within FPGAs (Field Programmable Gate Arrays) known as “partial¬†reconfigurable” regions – areas of the logic fabric that can be¬†loaded with new bitstream configs. Part of the discussion around¬†the latest patches centered on their providing a new sysfs¬†interface for loading FPGA images, and in particular the need¬†to ensure that this ABI handle FPGA bitstream metadata in a¬†standard and portable fashion across different OSes.

Intel 5-level paging

Kirill A. Shutemov posted version 3 of Intel’s 5 level paging¬†patch series that expands the supportable VA (Virtual Address)¬†space on Intel Architecture from 256TiB (64TiB physical) to¬†128PiB (4PiB physical). Channeling his inner Bill Gates, he¬†suggests that this “ought to be enough for anybody”. Key¬†among the TODO items remains “boot-time switch between¬†4 and 5-level paging” to avoid the need for custom kernels.¬†The latest patches introduce two new prctl calls to manage¬†the maximum virtual address space available to userspace¬†processes during mmap calls (PR_SET_MAX_VADDR and PR_GET_MAX_VADDR).¬†This is intended to aid in compatibility by preventing certain¬†legacy programs from breaking when confronted with a 56-bit¬†address space they weren’t expecting. In particular, some JITs¬†use high order “canonical” bits in existing x86 addresses to¬†encode pointer tags and other information (that they should not¬†per a strict interpretation of Intel’s “Canonical Addressing”).


Steven Rostedt announced verious preempt-rt (“Real Time”) kernel trees (4.4.47-rt59,¬†4.1.38-rt45, 3.18.47-rt52, 3.12.70-rt94, and 3.10.104-rt118).¬†Sebastian Andrzej also announced version v4.9.9-rt6 of the preempt-rt¬†“Real Time” Linux patch series. It includes fixes for a spurious¬†softirq wakeup, and a GPL symbol issue. A known issue is that¬†CPU hotplug can still deadlock.

Junio C Hamano announced version v2.12.0-rc2 of git.


Hoeun Ryu posted version 6 of a patch that takes care to properly¬†free up virtually mapped (vmapped) stacks that might be in the¬†kernel’s stack cache when cpus are offlined (otherwise the kernel¬†was leaking these during offline/online operations).

New Drivers

Mahipal Challa posted version 2 of a patch series implementing a¬†compression driver for the Cavium ThunderX “ZIP” IP on their¬†64-bit ARM server SoC (System-on-Chip) to plumb into the¬†kernel cryptoapi.

Anup Patel posted version 3 of a patch implementing RAID offload
support for the Broadcom “SBA” RAID device on their SoCs.

Ongoing Development

Andi Kleen posted various perf vendor events for Intel uncore devices, Kan Liang posted new core events for Intel Goldmont, and Srinivas Pandruvada posted perf events for Intel Kaby Lake.

Velibor Markovski (Broadcom) posted a patch implementing ARM Cache Coherent Network (CCN) 502 support.

Sven Schmidt posted version 7 of a patch series updating the LZ4¬†compression module to support a mode known as “LZ4 fast”, in¬†particular for the benefit of its use by the lustre filesystem.

Zhou Xianrong posted a patch (for the ARM Architecture) that attempts to save kernel memory by freeing parts of the the linear memmap for physical PFNs (page frame numbers) that are marked reserved in a DeviceTree. This had some pushback. The argument is that it saves memory on resource constrained machines Р6MB of RAM in the example.

Jessica Yu (who took over maintaining the in-kernel module loader infrastructure from Rusty Russell some time back) posted a link to her module-next tree in the kernel MAINTAINERS document.

Bhupesh Sharma posted a patch moving in-kernel handling of ACPI BGRT (Boot(time) Graphics Resource) tables out of the x86 architecture tree and into drivers/firmware/efi (so that it can be shared with the 64-bit ARM Architecture).

Jarkko Sakkinen posted version 2 of a patch series implementing¬†a new in-kernel resource manager for “TPM spaces” (these are¬†“isolated execution context(s) for transient objects and HMAC¬†and policy sessions.”. Various test scripts were provided also.

That’s all for this week. Tune in next time for the latest happenings in the Linux kernel community. Don’t forget to follow us @kernelpodcast

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