Linux Kernel 2.6.24 Released

LinuxFan writes "Linus Torvalds has released the 2.6.24 Linux Kernel, noting that he and most of the other key Linux developers will be flying to a conference in Australia for the next week. As the whole team will be down under while the kernel is being tested by the masses, Linus added, "Let's hope it's a good one". What's new in the latest release includes an optimized CFQ scheduler, numerous new wireless drivers, tickless kernel support for the x86-64 and PPC architectures, and much more. Time to download and start compiling."

Comments

Wow. Lots of stuff.

[MostAwesomeDude]

On one hand, things like the VM dirty writeback adjustments and default cpufreq frequency governors, as well as dynticks for more arches, are big performance improvements. On the other hand, they broke wireless packet injection patches for a lot of drivers... At any rate, I'll have to try this just to see if it really performs better. Things like laptop_mode which rely on optimized scheduling and writeback code should see improvements.

Re:Merge Window?

[iMaple]

There is a chance that some stupid airline CEO decided that their planes use The Evil Darklord's software for navigation. Of course we all know that noone would NEVER code a special condition in the software which says

if(passenger_list.contains(entire_linux_kernel_team){
      flyinto(mount_everest);
      output_evil_voice("muhahahhaa");
}

On the other hand, there is nothing to worry about. This feature probably was shelved and is definitely going to be in the *next* version of the OS.

Yeah tick less is fine stuff

[emj]

Reducing wakups on laptops is very interesting suff, I've seen some post on how muche better the NO_HZ is making things, e.g. Ross went from 164w/s to 5w/s just waking up 5 times per second makes the CPU pretty cool...

Re:tickless kernel support?

[MostAwesomeDude]

Can anyone explain to me what "tickless kernel support" is? Sure. Basically, instead of having a regular tick in the kernel every handful of cycles to process interrupts and timers, processes are given long, dynamic timers with arbitrary lengths, which means that if an app wants to sleep for a relatively long period, it gets to sleep and not wake up the CPU, so the CPU sleeps longer and a lot of power is saved.

I am really grateful for this release

[eclectro]

The weekend is almost here, and I am looking for something to do. I want to argue about the scheduler.

Re:I am really grateful for this release

[ajs318]

Let us also digress into a micro-kernel vs monolith-kernel discussion.

Oh, that's an easy one. With a microkernel, you put up fences where they look pretty. With a monolithic kernel and loadable modules, you put up fences where as little stuff as possible has to traverse them. Ting! Next, please.

Re:I am really grateful for this release

[nagora]

Arguments are down the hall.

No they aren't!

Anti-Fragmentation?

[kripkenstein]

The updates most interesting to me are the anti-fragmentation patches,

Tests show that about 60-70% of physical memory can be allocated on a desktop after a few days uptime. In benchmarks and stress tests, it has been found that 80% of memory is available as contiguous blocks at the end of the test. To compare, a standard kernel was getting ~1% of memory as large pages on a desktop and about 8-12% of memory as large pages at the end of stress tests.

Perhaps someone can clarify exactly what this means? Reading the beginning, it talked about 4K pages, device drivers, and such, so I assumed it would just be relevant to the internal workings of the kernel. However, the quote I pasted above seems to indicate it might impact desktop performance as well.

I commonly see on my desktop, after several days uptime, that quite a lot of memory is being used (and I know how to ignore cache/buffers, as well as swapcache - that isn't the issue). Logging out and logging back in returns memory to reasonable levels (and the system becomes more responsive, but then I guess if I bought more memory I could accomplish that as well). Now, I've generally read that the problem was indeed memory fragmentation, e.g. here, but this would be internal fragmentation inside an app, and thus not relevant to the kernel, I believe? If someone can explain this issue I'd be grateful.

Re:Anti-Fragmentation?

[Anonymous Coward]

He's talking about how the memory blocks allocated to user programs are actually laid out in physical memory. Think of it like this: if we have programs A, B, C, and D using memory (and F for free), before the physical memory may have been allocated something like this:
AAFBBFABCFCDBACDDBAF (not contiguous)

And now more like this:
AABBBAFFFCCCCDDFFFFF (free memory is in large contiguous chunks)

This is not something that userspace programs will notice directly, but it does affect performance of the machine. Keeping free space and other areas contiguous allows for better caching performance and faster access.

Re:Merge Window?

[Aladrin]

Did you seriously just managed to misspell both words in 'News Bulletin'?

Re:Merge Window?

[Anonymous Coward]

DId you seriously just manage to screw up correcting someone else?

eCryptfs persistent files

[omnirealm]

In 2.6.24, eCryptfs overhauled its I/O mechanism with the lower filesystem (check out fs/ecryptfs/read_write.c). It used to directly manipulate the lower inode address mappings, which caused problems with certain filesystems like NFS (they like to be the only filesystems directly locking, reading, and writing their own address mappings). Now it opens a persistent lower file for each and every stacked inode and uses that for all I/O with the lower filesystem. This significantly decreases the complexity of the execution path for reading and writing the lower data. Together with this patch, eCryptfs now works pretty well on networked filesystems like NFS and CIFS.

There is another patch to provide HMAC integrity enforcement, and the kernel GIT tree for eCryptfs has a branch indicating that filename encryption is being worked on.

Re:Merge Window?

[arkhan_jg]

DId you deliberately screw up that correction of a correction? You did, didn't you.

Re:Catching up to Windows on power

[ThePhilips]

It is sad reality the people keep mixing up technology and products.

Linux (as kernel and piece of technology) is far ahead of most OSs in power management and especially in power saving.

But. Take fresh Windows XP installation - it would give you decent up-time from single battery charge. Take Mac OS X - it would give you excellent up-time from single battery charge. Now take Linux's distro with X.Org/GNOME/KDE/etc - and it would eat any battery in under two hours.

It is possible to optimize Linux to be extremely power efficient, yet lion share of applications written for PCs simply fail on portables.

From recent example. I'm reading lots of PDF ebooks - under Mac OS. Trick is to scroll document to the end and then go back to place were you stopped: Mac OS would cache the file and hard drive will not wake up for the whole time you read thru the PDF. Linux? - Ubuntu/Kubuntu/SUSE/YellowDog were tried - hard drive is always spinning. Always. Non-stop. I stopped even trying to investigate what keeps it spinning - just went back to Mac OS. Because battery lasts under Linux for about 2 hours - while Mac OS on the aging iBook easily does 6 hours. But honestly, even if battery charge set aside, the noise produced by constantly spinning hard drive me slowly crazy.

Conclusion: excellent power management of kernel != end-user application are designed with power efficiency in mind.

P.S. Most common offenders are X.Org with its ~/.xsession-errors (as if end-users cared about all the cruft in there - developers simply do not look there at all) and syslogd which periodically (by default every 20 minutes) write marker into logs.