The 3.16 kernel has been released

> a CPU can be _completely_ assigned to a thread, without ANY kernelspace interrupts

Yep that is true and it is true not only on Linux.
However if such thread will start exchanging/sharing data with other threads such workload will enter on area where bottleneck will be not CPU but interconnect between cores/CPUs.
Try to have look on https://www.kernel.org/pub/linux/kernel/people/paulmck/pe... chapter 5.1 "Why isn't concurent conting trivial?"

If you are expecting that on your computations will be not interconnects intensive will you can relatively cheap build supercomputer. Problem is that in many cases you must deal with memory or interconnect intensive workloads. If your computations will be on interconnect intensive area you will have definitely many problems with locking and synchronization between threads and here OS may help. On diagnosing such problems you will need good instrumentation integrated with profiler. Tools like DTrace can do many things here. BTW .. on Linux still there is no cpc provider (CPU Performance Counter) https://wikis.oracle.com/display/DTrace/cpc+Provider

Interconnect intensive workloads are not only a HPC problems.

Of course is able and this is what exactly I wrote.
Problem is that on I found in few seconds just after first login executing as first command "dmesg | grep -i err" that factory default BIOS settings are not optimal/wrong.
On Linux you will see only different ACPI many lines reports. No errors or warnings.
It is very easy to overlook this on Linux. On Solaris looks like it is almost impossible to make similar mistake.
OK it is small detail but it is very good example of some development culture which is lack on Linux creates many of these "thousands cuts".

It is matter of ergonomy and thinking on development stage not to report Everything(tm) but first to report only crucial informations with some exact severity level.

Typical Linux dmesg output just after reboot is incredibly long. Reporting everything with high verbosity level in Linux case makes such things like incorrect HW PM issues harder to find if you don't know about what about you are looking for. Initial kernel logs should be only in single lines like:
found A
found B
..

And additional lines per module or hardware components in case some issues/errors/etc.
Lets have a look on Linux:

$ lsmod | wc -l
58
$ lspci | wc -l
38

but ..

$ wc -l /var/log/dmesg
770 /var/log/dmesg

And now dmesg on the same hardware under Solaris where all HW components are fully supported as well (just after reboot):

$ dmesg | wc -l
192

Now .. try to think about test script fired automatically just after OS (re)install which should catch as many as possible problems/issues. In case Solaris in 99% cases "dmesg | grep -i err" or dmesg | grep -i warn" is enough.
On linux it *is* really way harder.

Devil sits really sometimes in small details.
On Solaris it is good verbosity level. On Linux every module can report even few pages reports .. only because *there is no standardisation* here (again: "running with empty barrels" syndrome) and lack of thinking that kernel messages may be useful sometimes if they will be formed using some exact convention.

Sorry but what you are talking about?
SF10/15/20/25K are long time after EOL and EOS. IIRC none of this hardware is supported by Sol 11.
Rewritten PM is part of Sol 11.

> Solaris on x86. Let's avoid this rare beast for now.

Why. IMO it is good example which shows that at the moment there is no gap here between Solaris and Linux.
Solaris has now base PM support implemented in way which makes very easy to extend it across any possible type of hardware components which is not the case in case of Linux.

> Had to shut down ~ 4 full M9000 plus the t2k and other stuff. All done entering inside the data center like a diver and getting out without getting burned

Again you are talking about quite old hardware. M9000 Sun started selling in April 2007. Try to compare this hardware with something equally old if you want to show something about PM.

This is like in real life. If someone will break a leg if rehabilitation will be OK someone may even fully recover. Try to spend huge part of your life walking with few small stones inside your shoe which you are not going to remove "because you are so busy".

In case btrfs someone should really kick off this fs from kernel tree.
Why? Yet another metaphor:
If few days ago NASA announced that they started testing EmDrive and no one today is thinking about using steam engine to make Solar system exploration possible. As same no one should be wasting time working on new Linux FS if it will be not using free list and few other new bits.