In cases where we have multiple models or threadpools active, spinning around
`sched_yield()` may not be desirable, as it prevents the OS from effectively
scheduling other threads.

Thus, allow users to conditionally disable this behaviour (via an environment
variable `TVM_THREAD_POOL_SPIN_COUNT`, similar to existing environment flags for
the thread pool such as `TVM_BIND_THREADS`, etc).

This substantially improves tail latencies in some of our multi-tenant
workloads in practice.

Unit tests have been added - on my laptop, running:

```
TVM_THREAD_POOL_SPIN_COUNT=0 ./build/threading_backend_test;
TVM_THREAD_POOL_SPIN_COUNT=1 ./build/threading_backend_test;
./build/threading_backend_test;
```

gives https://gist.github.com/ajtulloch/1805ca6cbaa27f5d442d23f9d0021ce6 (i.e.
97ms -> <1ms after this change)

* [RFC] Initial support for Tflite operator SPLIT

This patch adds initial support for the tflite operator split. However
I am not yet sure how to handle the axis parameter for the split
operator and support it in the test infrastructure. Putting this up for
an initial review and comment.

The split operator in tflite according to
https://www.tensorflow.org/lite/guide/ops_compatibility

appears to take num_or_size_split as a 0D tensor.

I also note that tflite.split is one of the few operators that returns
multiple outputs and thus the helper routines in the tests needed some
massaging to make this work.

@apivarov , could you please review this ?

Thanks,
Ramana

* Fix the axis parameter

Add more tests

* Address review comments

* Try out frozen_gene's suggestion

* Handle split of 1 element

* int32 is only supported in tflite 1.14, let's check that version here.

* Keep this at python3.5

* Add packaging as a python package to be installed

* updated runtime to support non-shared memory FPGAs for instruction and micro-op kernels

* adding driver-defined memcpy function to handle F1 cases

* refactor to include flush/invalidate in memcpy driver function

* update tsim driver

* bug fixes

* cleanup

* pre-allocate fpga readable buffers to improve perf

* fix

* remove instruction stream address rewrite pass for micro op kernels

* fix:

* white spaces

* fix lint

* avoid signed/unsigned compilation warning

* avoid signed/unsigned compilation warning

* fix

* fix

* addressing comments

* whitespace

* moving flush/invalidate out of memmove

* clearnup

* fix

* cosmetic

* rename API

* comment fix

* do

* fix test

* Improve boundary nodes in graph tuner

* Limit output node number

* Fix test

* Improve warning.

* Fix test

* Support additional architectures beyond x86_64 in ubuntu_install_java

While attempting to get a development environment going for TVM
on my AArch64 desktop I ran into some hardcoding of relevant architectures.

Let's welcome Zhi as a new Apache TVM Committer!

Apply suggestions from code review

Co-Authored-By: Wei Chen <ipondering.weic@gmail.com>

* [docs] Add a tutorial for the pass manager

* address comment

* address more comments

* retrigger ci

* address steven's comments

* address comments

* retrigger ci

* Update docs/dev/relay_pass_infra.rst

Co-Authored-By: Steven S. Lyubomirsky <slyubomirsky@gmail.com>

* Update docs/dev/relay_pass_infra.rst

Co-Authored-By: Steven S. Lyubomirsky <slyubomirsky@gmail.com>

* Update docs/dev/relay_pass_infra.rst

Co-Authored-By: Steven S. Lyubomirsky <slyubomirsky@gmail.com>

* Update docs/dev/relay_pass_infra.rst

Co-Authored-By: Steven S. Lyubomirsky <slyubomirsky@gmail.com>

* Update docs/dev/relay_pass_infra.rst

Co-Authored-By: Steven S. Lyubomirsky <slyubomirsky@gmail.com>

* Update docs/dev/relay_pass_infra.rst

Co-Authored-By: Logan Weber <36520469+weberlo@users.noreply.github.com>

* Update docs/dev/relay_pass_infra.rst

Co-Authored-By: Logan Weber <36520469+weberlo@users.noreply.github.com>

* [Relay][VM]Fix debug statement

* Change debug statement

* Fix build error

* comments

* tmp

* Port vm and object to python

* clean up

* update vm build module

* update

* x

* tweak

* cleanup

* update

* fix rebase

* Rename to VMCompiler

* fix

* Enable set_input_zero_copy in GraphRuntime

* Fix LoadParams

* Fix

* lint

* Fix remote context issue

* Fix

* Remove LOG

* Remove unused variables

* Add tests

* works

* More test scenarios

* make it simpler

* Remove unnecessary changes

* Address comments

* More comments

* Address comments

* Fix build

* [TVM] Fix bound inference to avoid allocating too much

* [ARITH][BOUND] Pass analyzer to PropBoundToInputs

* [ARITH][IR] Introduce FloorDiv/Mod

* Address review comments

* address review comments, fix div sub rule

* [Relay][Quantization] Fix issue introduced in #3135

* Recover StopFusion

* Fix fmultiref

* Fix lint

* [INFA][IR] Build and Evolve Low-level IR. Remove dep from HalideIR.


* Update include/tvm/node/ir_functor.h

Co-Authored-By: Jared Roesch <roeschinc@gmail.com>

* Update include/tvm/node/ir_functor.h

Co-Authored-By: Jared Roesch <roeschinc@gmail.com>