Monday, November 23, 2020

Video: Powered Parachute Flying by the Cabin

Pretty cool video of someone having a nice sunset float in the sky over Lake Travis.  Taken November 21, 2020.


Video: Felling an Oak Tree at My Cabin

Here is a video of me having fun with my chain saw.  This is one of the several trees we took down around my cabin to make way for new construction.  Luckily I still have lots of good oaks remaining on the lot.


Monday, November 16, 2020

Computer Architecture: Efficient Micro Parallel Synchronization Mechanisms

I have often wondered why modern computer instruction set architectures do not have more efficient parallel synchronization mechanisms.  Current mainstream microprocessor designs currently support two types of parallelism.

  • Very fine grain
    • Hardware based implicit instruction level
    • Implemented via advanced pipeline register renaming.
    • Synchronization delays on the order of a single cycle.
  • Very course grain
    • Software based explicit thread synchronization primitives
    • Implemented via atomic memory instructions.
    • Synchronization delays on the order of tens of thousands of cycles or more.
With CPU clock frequencies beginning to plateau it may be time to revisit architectural synchronization models as a method to continue improving overall program performance.  If we have any bright PHD candidates reading this fishing for a dissertation topic, please consider this.

Parallel Architecture Models

At the process level we have the architectural notion of an interrupt.  But at the thread level this does not exist.  We have to rely on threads spinning in a loop reading and writing a shared memory location together with memory synchronization barriers and no architectural specification about how long this can take.  This is ridiculous.  We can't have efficient parallel programming if the programming model has no mechanism to facilitate it.  We need some data queue or message passing mechanism or interrupt that operates at the instruction architecture level if we are to enable efficient parallel programming.

Explicit Instruction Level Parallelism

I would like to see an efficient software visible instruction level synchronization mechanism.  For example, something like a 'Queue Register'.  Some existing IO registers track read and write state.  I'm thinking some general purpose registers could similarly be architected for managing data flow synchronization at the register data level.  Such registers could essentially stall the execution pipeline on reads until a write to that register has occurred.  So the register effectively acts as a 'data queue' at the instruction execution level.  This would enable software control of fine grain parallelism, opening up potentially more real parallelism than relying on hardware to extract parallelism from an inherently sequential programming model.

Since all compute state needs to be visible in order to stop, save, and later restart a process, status bits will also need to track the read/write data state of each queue register.  CPU pipelines could be redesigned to key off of these explicit reg data states, instead of implicit internal hardware states.  Just like current hardware threads swap in whichever thread has data ready, these new threads could work the same way.  The primary difference being the data ready state is now software architecturally visible.

Further note that these hardware queue registers are effectively thread state ready registers, analogous to ready state flags in operating system thread schedulers.  Since these ready flags are intended for micro data level parallelism, they should be closely aligned to the real register thread state supported by the hardware, as opposed to some arbitrary virtual state that relies on time slicing and swapping threads in and out of hardware.  While time slicing is theoretically possible it would blow up performance by 10000 times, entirely defeating the advantage of micro level parallelism.

So there is a different mind set when programming this level of parallelism.  This type of parallelism should have some awareness of the number of hardware threads efficiently supported by hardware, as opposed to some very course grain parallelism that has little concern about real hardware thread counts.  The implication is that this level of coding is more appropriate for hand coded assembly or for compilers.


Politics: The Political Divide (Urban verses Rural)

The 2020 US presidential election is over and it looks like Joe Biden will be replacing Donald Trump as the next US president.  From what I've gathered from the talking heads on network TV and the internet there is a lot of angst about our deeply divided country.  Some even talk about doing away with the Electoral College.  

When I look at the electoral results map it is blindingly painfully obvious that conservative red districts are rural, and liberal blue districts are urban.  This makes perfect sense to me so I don't get why this is so hard for the major media talking heads to understand.  A rural farmer living on a 100 acre farm by absolute necessity has to be far more self sufficient and independent than a desk jockey living in a high rise condo in a large metropolis.  Duh.  This ain't rocket science. 

If you live on a rural farm, and someone is breaking into your house in the middle of the night, you don't hide in the closet and dial 911, you grab your gun and deal with it.  Waiting an hour for the sheriff to arrive is not an option, especially if you have family.  

When you're plowing your field and your tractor breaks down you get your toolbox and start diagnosing what is wrong.  Why ?  Because waiting a week for a repairmen is not an option for your crop schedule or your wallet.

Global warming ?  That is concerning, but more concerning right now for the working rural poor are their bleeding knuckles and what their family is going to eat tonight.

So can we please stop demonizing the working rural poor who voted for less federal bureaucracy and more job security in their lives ?  Donald Trump may be a narcissistic self serving ass, but that doesn't mean he is always wrong.  Let's not forget there is a reason he got elected for his first term.

And regarding the Electoral College, this is the mechanism that the framers of the constitution came up with to balance out the rural state needs with the urban population focused house of representatives.  Anyone who talks about scrapping the Electoral College without some other mechanism to represent the working rural poor is risking disenfranchising the working rural poor.  That is self serving, oppressive, and potentially grounds for civil war, so uh, probably not a good idea.

So please remember, we don't all live in high rise urban condos and have high paying jobs.