Het heeft meer tijd gekost dan verwacht werd, maar Linus Torvalds heeft gisteravond op de Linux Kernel Mailing List een nieuwe 2.6-kernel aangekondigd. Het gaat dit keer om versie 2.6.21 die de in begin februari uitgebrachte 2.6.20-release opvolgt en vanaf deze Nederlandse mirrorserver gedownload worden. De 2.6.20-versie bracht veel nieuwe features en ingrijpende veranderingen met zich mee waaronder Kernel-based Virtual Machine, waarvoor de nieuwe .21-branch verbeteringen kent. Daarnaast zijn er verbeteringen doorgevoerd voor een betere ondersteuning van de PlayStation 3, Wat er zoal veranderd is in Linux-kernel 2.6.21 kan gelezen worden op KernelNewbies, of hieronder:
If the goal for 2.6.20 was to be a stable release (and it was), the goal for 2.6.21 is to have just survived the big timer-related changes and some of the other surprises (just as an example: we were apparently unlucky enough to hit what looks like a previously unknown hardware errata in one of the ethernet drivers that got updated etc).
So it's been over two and a half months, and while it's certainly not the longest release cycle ever, it still dragged out a bit longer than I'd have hoped for and it should have. As usual, I'd like to thank Adrian (and the people who jumped on the entries Adrian had) for keeping everybody on their toes with the regression list - there's a few entries there still, but it got to the point where we didn't even know if they were real regressions, and delaying things further just wasn't going to help.
So the big change during 2.6.21 is all the timer changes to support a tickless system (and even with ticks, more varied time sources). Thanks (when it no longer broke for lots of people ;) go to Thomas Gleixner and Ingo Molnar and a cadre of testers and coders.
Of course, the timer stuff was just the most painful and core part (and thus the one that I remember most): there's a lot of changes all over. The appended changelog is just for the fixes since -rc7, so that doesn't look very impressive, the full changes since 2.6.20 are obviously a *lot* bigger (and you're better off reading the individual -rc changelogs).
We now return you to your regular scheduler discussions,
2.6.21 improves the virtualization features merged in 2.6.20 with VMI (http://lwn.net/Articles/175706), a paravirtualization interface that will be used by Vmware (and maybe -probably not- Xen) software. KVM does get initial paravirtualization along with live migration and host suspend/resume support (http://lwn.net/Articles/223839). 2.6.21 also gets a tickless idle loop mechanism called "Dynticks" (http://lwn.net/Articles/223185), a feature built in top of "clockevents" which unifies the timer handling and brings true high-resolution timers. Other features are: bigger kernel command-line, optional ZONE_DMA; support for the PA SEMI PWRficient CPU, for a Cell-based "celleb" architecture from Toshiba, better PS3 support: support for NFS IPv6, IPv4 <-> IPv6 IPSEC tunneling support, UFS2 write support, kprobes for PPC32, kexec and oprofile for ARM, public key encription for ecryptfs, Fcrypt and Camilla cipher algorithms, NAT port randomization, audit lockdown mode, many new drivers and many other small improvements.