
Linux 4.9 is out - sply
https://lwn.net/Articles/708766/
======
gtirloni
For anyone wondering, 4.9 is expected to be the next LTS kernel:

[http://kroah.com/log/blog/2016/09/06/4-dot-9-equals-
equals-n...](http://kroah.com/log/blog/2016/09/06/4-dot-9-equals-equals-next-
lts-kernel/)

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sandGorgon
kernel 4.9 is the first kernel with full dynamic tracing support built in
(beyond the power of systemtap, etc) . We are soon going to see tools like
dtrace being built right for Linux.

Im excited for thw future of application development and monitoring on Linux.
Imagine a whole bunch of tools more powerful than NewRelic.

~~~
aktau
Interesting, I assume you're referring to some extension of eBPF that happened
in the 4.9 pulls. AFAIK eBPF already is pretty functional in 4.8. What got
added that allows full dynamic tracing? (And what is full dynamic tracing?).

EDIT: Parent is probably referring to something mentioned here:
[http://www.brendangregg.com/blog/2016-10-27/dtrace-for-
linux...](http://www.brendangregg.com/blog/2016-10-27/dtrace-for-
linux-2016.html). Apparently timed sampling got added, I quote Brendan:

> Timed sampling was the final major piece, and it landed in Linux 4.9-rc1
> (patchset). Many thanks to Alexei Starovoitov (now working on BPF at
> Facebook), the lead developer behind these BPF enhancements.

This is indeed something possible with DTrace that was difficult (or not very
efficient) to do with eBPF before. I assume one could've hooked into one of
the kernel interrupt/... functions and used that as a ghetto timer, but the
gymastics to convert that to real time might've been daunting.

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mparlane
The amount of times the word "updates" appears in the commits makes me feel
much better at my difficulty of choosing succinct and unique commit messages.

~~~
anarazel
Note that those aren't "change commits", but merge commits aggregating large
swathes of other changes. And it's not even all merge commits, it's just the
merges from Linus' "top lieutenants".

But I sympathize. I often spend more time on commit messages than the actual
changes...

~~~
wolfgang42
Writing long commit messages (especially for internal/private projects) often
gives me a slightly forlorn feeling, knowing that these words will almost
certainly never be read again by another person, and possibly even I might
never see them again. I persist only because when they _do_ get read, they can
be absolutely invaluable in explaining what on earth I was thinking at the
time.

~~~
grzm
_I persist only because when they do get read, they can be absolutely
invaluable in explaining what on earth I was thinking at the time._

I wish I could upvote this more than once.

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agumonkey
I remember reading about bufferbloat related patches in 4.9 that would make
network quite a lot more efficient. Curious to see in practice.

~~~
sanxiyn
BBR congestion control is amazing. You can read about it here:
[http://queue.acm.org/detail.cfm?id=3022184](http://queue.acm.org/detail.cfm?id=3022184)

~~~
agumonkey
The team made a talk recently, I'll url it when I get back.

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aseipp
Intel memory protection key support is nice. QEMU now also has support for
emulation of pkeys, but naturally you can't use them with KVM/hw acceleration
(because you don't have hardware to support them). This is generally enough
for testing/designing, though. (The performance of memory protection keys will
be important however, so it's not helpful to really determine that yet.)

That said, I'd suggest obviously building your own minimal kernel/chroot to do
these tests, since the lack of KVM/available hardware makes emulation turn-
around time fairly terrible for right now.

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voltagex_
Still no sign of NVMe "RAID" support:
[http://marc.info/?t=147709622400002&r=1&w=2](http://marc.info/?t=147709622400002&r=1&w=2)

~~~
wtallis
There's already a patch (due for 4.10) to detect and warn about this
silliness. Since the Intel guy says that all the systems that shipped with
this mode now have firmware updates to allow disabling it, there's very little
reason for anyone to implement full support.

Hopefully in the future Intel will think twice before implementing ugly
firmware-level hacks to aid in working around limitations of Microsoft's
driver stack.

~~~
voltagex_
What real world impact does changing from (fake) RAID to AHCI have?

~~~
wtallis
That's the firmware setting that disables the hack that hides NVMe devices
behind the chipset's AHCI controller. Aside from making it possible for
standards-compliant NVMe drivers to function as expected, not lying to the OS
about the hardware topology also allows the OS to access the PCI configuration
space (allowing for eg. ASPM support) and not unnecessarily share interrupts
between two entirely separate devices.

~~~
voltagex_
So it'd be better for Linux to support this RAID/NVMe mode natively, right?

~~~
wtallis
If it served a useful purpose in the first place, yes. And if it were properly
documented and didn't cripple certain areas of functionality (and probably
hurt performance a bit, but I don't yet have a system to measure this with).

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ajdlinux
The Kernel Newbies LinuxChanges page hasn't been updated yet, but when it is,
it'll be at
[https://kernelnewbies.org/LinuxChanges](https://kernelnewbies.org/LinuxChanges).

~~~
voltagex_
Should I be worried about Kernel Newbies? The forum is overrun by spam and it
looks like the wiki wasn't updated for 4.8.

~~~
koolba
I've never read the forum but the kernel summaries are fantastic.

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lucb1e
I wonder what "DRM updates" and "DRM fixes" include.

~~~
Arcaire
DRM there refers to Direct Rendering Manager[0].

A few days ago the author those changes are listed under (Dave Airlie) was on
the HN frontpage for his comments on an AMD RFC[1].

[0]
[https://en.wikipedia.org/wiki/Direct_Rendering_Manager](https://en.wikipedia.org/wiki/Direct_Rendering_Manager)

[1]
[https://news.ycombinator.com/item?id=13136426](https://news.ycombinator.com/item?id=13136426)

~~~
ramy_d
so when the AMD patch was refused, it was refused for this LTS version of the
kernel? that's gotta be a huge blow against AMD, no?

~~~
wtallis
The merge window for 4.9 closed long before this recent spate of publicity.
The AMDGPU patch would have been on track for more like 4.11.

~~~
ramy_d
ah ok, thanks for the information.

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terrywang
Now the corresponding Linux Kernel Newbies page takes ages to be updated and
reflect the changes ;-(

------
known
"make localmodconfig" in case you're compiling the kernel

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zzzzz99997
Why are Linux changelogs so unbelievably shitty? I read it and I have no idea
what changed. But, hey, at least I know who fucking changed it, right?

~~~
wolfgang42
The problem, as I understand it, is that these are summaries of summaries. The
actual commit messages are incredibly detailed, then they get rolled up by the
lieutenants into a single merge with one line per change, then Linus merges
them in and adds to the final summary 'networking updates'. If you want to
know what actually changed, then look at the commit logs, e.g.:

[https://github.com/torvalds/linux/compare/v4.9-rc8...v4.9](https://github.com/torvalds/linux/compare/v4.9-rc8...v4.9)

