Jeff Garzik posted a series of nine patchs to the lkml titled to "remove [the] 'irq' argument from all irq handlers", explaining, "the overwhelming majority of drivers do not ever bother with the 'irq' argument that is passed to each driver's irq handler. Of the minority of drivers that do use the arg, the majority of those have the irq number stored in their private-info structure somewhere." He noted that he had no intention to push the patches upstream anytime soon.
Feedback was entirely positive, with Thomas Gleixner suggesting, "Full ACK. We should do this right at the edge of -rc1. And let's do this right now in .24 and not drag it out for no good reason." Ingo Molnar concurred, "full ACK on the concept from me too. Please go ahead! :)" Eric Biederman noted that there was still work to be done, "the practical question is how do we make this change without breaking the drivers that use their irq argument." Jeff agreed, explaining why the code won't be pushed upstream during -rc1, "I am finding a ton of bugs in each get_irqfunc_irq() driver, so I would rather patiently sift through them, and push fixes and cleanups upstream. Once that effort is done, everything should be in the 'trivial' pile and not have the logic that you are worried about (and thus there would be no need to add an additional branch to the irq handling path)."
"I said I was hoping that -rc8 was the last -rc, and I hate doing this, but we've had more changes since -rc8 than we had in -rc8. And while most of them are pretty trivial, I really couldn't face doing a 2.6.23 release and take the risk of some really stupid brown-paper-bag thing," Linus Torvalds said, announcing the 2.6.23-rc9 kernel. He added, "so there's a final -rc out there, and right now my plan is to make this series really short, and release 2.6.23 in a few days. So please do give it a last good testing, and holler about any issues you find!" He went on to warn developers that the first thing planned for 2.6.24 was to merge the unified x86 architecture:
"This is also a good time to warn about the fact that we're doing the x86 merge very soon (as in the next day or two) after 2.6.23 is out, so if you have pending patches for the next series that touch arch/i386 or x86-64, you should get in touch with Thomas Gleixner and Ingo Molnar, who are the keepers of the merge scripts, and will help you prepare..
"Doing it as early as possible in the 2.6.24-rc4 series (basically I'll do it first thing) will mean that we'll have the maximum amount of time to sort out any issues, and the thing is, Thomas and Ingo already have a tree ready to go, so people can check their work against that, and don't need to think that they have to do any fixups after it his *my* tree. It would be much better if everybody was just ready for it, and not taken by surprise."
"Ok, I think I'm getting close to releasing a real 2.6.23," began Linus Torvalds in his release announcement for the eighth release candidate of the upcoming 2.6.23 kernel. "Things seem to have calmed down, and I think Thomas Gleixner may have found the suspend/resume regression that has dogged us for a while, so I'm feeling happy about things." Linus continued:
"Of course, me feeling happy is usually immediately followed by some nasty person finding new problems, but I'll just ignore that and enjoy the feeling anyway, however fleeting it may be.
"The shortlog really is pretty short, and I'm appending the diffstat at the end too in case anybody cares, but basically it's just a number of fairly small but real fixes, with some support for a few new chips to the sky2 network driver.."
"It took me quite a while to realize the real root cause of the VAIO - and probably many other machines - suspend/resume regressions, which were unearthed by the dyntick / clockevents patches," Thomas Gleixner explained regarding two patches for fixing suspend issues that Andrew Morton experienced with his VAIO laptop. He continued, "we disable a lot of ACPI/BIOS functionality during suspend, but we keep the lower idle C-states functionality active across suspend/resume. It seems that this causes trouble with certain BIOSes, but I assume that the problem is more wide spread and just not surfacing due to the various scenarios in which a machine goes into suspend/resume." Thomas concluded, "I really hope that this two patches finally set an end to the 'jinxed VAIO heisenbug series', which started when we removed the periodic tick with the clockevents/dyntick patches."
Linus Torvalds expressed some concerns, "the patches look fine, but I somehow have this slight feeling that you gave up a bit too soon on the '*why* does this happen?' question." He agreed that at that point there was a problem with ACPI, but cautioned that this could be triggered by another bug, "in particular, I also suspect that this may not really fix the problem - maybe it just makes the window sufficiently small that it no longer triggers. Because we don't necessarily understand what the real background for the problem is, I'm not sure we can say that it is solved." Linus concluded, "but hey, I think I'll apply the patches as-is. I'd just feel even better if we actually understood *why* doing the CPU Cx states is not something we can do around the suspend code!"
Thomas Gleixner described an effort to create a unified x86 architecture tree, "the core idea behind our project is simple to describe: we introduce a new arch/x86/ and include/asm-x86/ file hierarchy that includes all the existing 32-bit and 64-bit x86 code and allows the building of either a 32-bit (i386) kernel or a 64-bit (x86_64) kernel." Andi Kleen expressed some concern, "I think it's a bad idea because it means we can never get rid of any old junk. IMNSHO arch/x86_64 is significantly cleaner and simpler in many ways than arch/i386 and I would like to preserve that. Also in general arch/x86_64 is much easier to hack than arch/i386 because it's easier to regression test and in general has to care about much less junk. And I don't know of any way to ever fix that for i386 besides splitting the old stuff off completely." Additional concerns about legacy issues were countered by Linus Torvalds, "there really isn't that much legacy crud. There are things like random quirks, but every time I hear the (theoretical) argument about how much time and effort we save by having it duplicated somewhere else, I think about all the time we definitely waste by fixing the same bug twice (and worry about the cases where we don't)." Among the justifications for a unified architecture, Thomas noted:
"We believe that the whole x86 CPU family is very much related and should be supported in a single architecture tree. All 64-bit CPUs implement the ability to execute pure 32-bit kernels, and will probably do so for the next couple of decades. So it's not like it will ever be possible to get rid of our legacies: for example even the latest 64-bit CPUs implement the legacy 'A20 line' feature that was already a weird outdated hack in the days of 16-bit x8086 CPUs."
Ingo Molnar announced that the real time patchset [story] that he and Thomas Gleixner maintain is now available as a series of 374 broken out patches, "from now on (as of 22.214.171.124-rt2) it will be part of every upstream -rt release and it is available from the -rt download site". Regarding the patches, he notes that it's responsible for, "698 files changed, 27920 insertions(+), 9603 deletions(-)", going on to note, "which is impressive as we moved a huge chunk of -rt into mainline already ;-) The series file is attached below.". Ingo explains:
"the purpose of this finegrained splitup is to foster (even ;-) quicker upstream integration of various -rt features, and to see the full -rt tree integrated upstream. We also hope that this split-up queue helps various vendors standardize their (currently quite splintered) real-time implementations to the upstream -rt patchset. The queue is not (yet) bisectable at every point, and many of the splits are thematic, to allow the simpler future handling of updates."
Included in Andrew Morton's potential 2.6.23 merge list [story] were a series of patches to make the x86-64 architecture tickless. Andi Kleen, the x86-64 maintainer replied, "I'm sceptical about the dynticks code. It just rips out the x86-64 timing code completely, which needs a lot more review and testing. Probably not .23." Linus Torvalds agreed, "we are *not* going to do another 'rip everything out, and replace it with new code' again. Over my dead body. We're going to do this thing gradually, or not at all." He went on to explain "the patch-set itself actually looks fine, as far as I'm concerned. But it does seem to have that 'enable everything in one go' problem. I'd much rather see one time source at a time being converted, and enabled then and there, so that when people report problems and do a bisection, if it was HPET that broke, you get the commit that changed HPET."
In response to the pains caused by the original dyntick merge in 2.6.21, Ingo Molnar acknowledged, "we had 12 -hrt/dynticks merge related regressions between 2.6.21-rc1 and -final, and 4 after final." He went on to point out, "it's all pretty quiet today on the dynticks regressions front. (there are no open regressions in either the upstream i386 code or in the devel patches we are aware of)." As to the source of the bugs, he explained, "the majority of the above bugs were in the infrastructure code. (the worst was the generic resume/suspend one fixed in 126.96.36.199) And sadly, a fair number of the infrastructure bugs we introduced during the frentic clockevents/dynticks rewrites/redesigns we did between .20 and .21. That was a royally stupid mistake for us to do - instead of patiently waiting for the bugs to be shaken out we destabilized the infrastructure. (it was a 'lets make this thing so nice that it's impossible to reject' instintic gut reaction.)" Linus replied, "one thing I'll happily talk about is that while 2.6.21 was painful, you and Thomas in particular were both very responsible about the thing, so no, I'm not at all complaining or worried about it in that sense! I just really _really_ wish we could have two fairly stable releases in a row. I think 2.6.22 has the potential to be a pretty good setup, and I'd really like to avoid having another 2.6.21 immediately afterwards."
Jörn Engel announced LogFS, "a scalable flash filesystem." The project's home page notes that LogFS aims to be the successor of JFFS2, "the two main problems of JFFS2 are memory consumption and mount time. Unlike most filesystems, there is no tree structure of any sorts on the medium, so the complete medium needs to be scanned at mount time and a tree structure kept in-memory while the filesystem is mounted. With bigger devices, both mount time and memory consumption increase linearly. JFFS2 has recently gained summary support, which helps reduce mount time by a constant factor. Linear scalability remains. YAFFS also appears to be better by a constant factor, yet still scales linearly."
In contrast, Jörn compared his new LogFS, "LogFS has an on-medium tree, fairly similar to Ext2 in structure, so mount times are O(1). In absolute terms, the OLPC system has mount times of ~3.3s for JFFS2 and ~60ms for LogFS." Regarding its stability, he noted, "LogFS works and survives my testcases. It has fairly good chances of not eating your data during regular operation. There are still two known bugs that will eat data if the filesystem is uncleanly unmounted. Also still missing is wear leveling." Thomas Gleixner reviewed the code and offered the following summary, suggesting the code has a ways to go before it replaces JFFS2, "the code is far from being useful on real world hardware. The error handling via BUG() is just making it useless. Also please fix the coding style and other issues from the seperate review. Some useful comments would make a functional review way easier."
Linux creator Linus Torvalds announced the release of the 2.6.21 kernel, "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)." Regarding the the dynticks code which was merged in -rc1 [story] he said, "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." He went on to note, "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)." Linus finished with a running joke about the many debates centered around current CPU scheduler efforts [story], quipping, "we now return you to your regular scheduler discussions".
Linus Torvalds announced the first release candidate for the upcoming 2.6.21 kernel, ending the two-week merge window [story], "there's a lot of changes, as is usual for an -rc1 thing, but at least so far it would seem that 2.6.20 has been a good base, and I don't think we have anything *really* scary here." Linus noted that the tickless kernel patch [story] was finally merged into the mainline kernel, "the most interesting core change may be the dyntick/nohz one, where timer ticks will only happen when needed. It's been brewing for a _loong_ time, but it's in the standard kernel now as an option." Thomas Gleixner explained a year ago how this could result in cooler CPUs and power savings, "the tickless kernel feature (CONFIG_NO_HZ) enables 'on-demand' timer interrupts: if there is no timer to be expired for say 1.5 seconds when the system goes idle, then the system will stay totally idle for 1.5 seconds."
As for the rest of the changes, Linus added, "there's a ton of architecture updates (arm, mips, powerpc, x86, you name it), ACPI updates, and lots of driver work. And just a lot of cleanups." Release candidate kernels can be downloaded from your nearest kernel.org mirror. You can browse through all the changes using the gitweb interface. Kernel Newbiews maintains a useful summary of all the changes going into the latest version of the Linux kernel.
Thomas Gleixner and Ingo Molnar [interview] posted an update of their high-res timers kernel patches for the 2.6.17 kernel, "upon which we based a tickless kernel (dyntick) implementation and a 'dynamic HZ' feature as well". The patch currently works for x86, with ports to x86_64, PPC and ARM in the works. Thomas explains, "the high-res timers feature (CONFIG_HIGH_RES_TIMERS) enables POSIX timers and nanosleep() to be as accurate as the hardware allows (around 1usec on typical hardware). This feature is transparent - if enabled it just makes these timers much more accurate than the current HZ resolution." He goes on to discribe the tickless kernel:
"The tickless kernel feature (CONFIG_NO_HZ) enables 'on-demand' timer interrupts: if there is no timer to be expired for say 1.5 seconds when the system goes idle, then the system will stay totally idle for 1.5 seconds. This should bring cooler CPUs and power savings: on our (x86) testboxes we have measured the effective IRQ rate to go from HZ to 1-2 timer interrupts per second.
"This feature is implemented by driving 'low res timer wheel' processing via special per-CPU high-res timers, which timers are reprogrammed to the next-low-res-timer-expires interval. This tickless-kernel design is SMP-safe in a natural way and has been developed on SMP systems from the beginning."