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Similar to the llama engine, quantizing the KV cache requires
flash attention to be enabled through the Ollama server.

Backends can impose additional alignment requirements on buffer sizes.
We should ensure that we meet these or allocations can fail.

this ensures the tensor is created on the right buffer type for backends
such as cpu

temporary until tensor loading can accurately account for vision models

some tensors should be created on specific backends to reduce number of
copies and improve performance

each cache layer creates and maintains its own context instead of using
a large context for all layers

some tensors are expected to be used in repeating layers but are not
themselves repeated. this change copies these tensors into the same
backends as their repeating counterparts to minimize copying tensors
between backends

use a similar strategy as llama.cpp for deciding where tensors should be
allocated. this will be improved later to be aware of usable memory
before assigning the tensor

- output backend system info when initializing the backend. this ensures
  this information is always present without needing to be called
  explicitly
- convert to structured logging
- enumerate devices rather than backends since devices are ordered
- track device indices grouped by device name

expand backend loading error handling to catch more problems and log
them instead of panicing

The GGML flash attention kernel has specific requirements for
padding and permutation. This adds support to the KV cache
for conforming to these requirements so that flash attention
can be enabled.

Flash attention can be used in the same situations as the llama
engine and is enabled by the user in the same way.

In cases where we allocate a tensor and then fully overwrite it with
copied data, it is wasteful to first zero out the memory.

It can be important for a tensor to know what backend it came from -
for example, to know if flash attention is enabled.

Prior to performing attention, we need to permute query, key
and value. Currently we call Contiguous after each of these
permutations, which is correct but expensive. Avoiding the
3 calls to Contiguous increases performance by over 20%.

The permutations of query and key do not violate the continuity
rules for mulmat and the Contiguous call can be simply removed.

Value requires a different permutation and does require Contiguous.
However, we can use the copy into the cache as a way to perform this
without further overhead.

To support this and avoid unexpected tensor shapes that are seen by
models, we need tighter integration between attention, cache
and backend. Future optimization will also likely need this structure
 - for example, flash attention has special padding requirements in
the cache and other backends may have their own needs.

This further contains the operations that go into attention so that
these and other optimizations can be handled transparently. Models
that have special requirements for attention can still implement
their own version of it.

update Context.Forward to accept multiple tensors to match
Context.Compute signature

update Context.Forward to return Context such that it can be chained
with Context.Compute

Fixes sync filters and lowers CUDA version to 11.3 in test.yaml

During work on our new registry client, I ran into frustrations with CI
where a misspelling in a comment caused the linter to fail, which caused
the tests to not run, which caused the build to not be cached, which
caused the next run to be slow, which caused me to be sad.

This commit address these issues, and pulls in some helpful changes
we've had in CI on ollama.com for some time now.

They are:

* Always run tests, even if the other checks fail.

Tests are the most important part of CI, and should always run. Failures
in tests can be correlated with failures in other checks, and can help
surface the root cause of the failure sooner. This is especially
important when the failure is platform specific, and the tests are not
platform independent.

* Check that `go generate` is clean.

This prevents 'go generate' abuse regressions. This codebase used to use
it to generate platform specific binary build artifacts. Let's make sure
that does not happen again and this powerful tool is used correctly, and
the generated code is checked in.

Also, while adding `go generate` the check, it was revealed that the
generated metal code was putting dates in the comments, resulting in
non-deterministic builds. This is a bad practice, and this commit fixes
that. Git tells us the most important date: the commit date along with
other associated changes.

* Check that `go mod tidy` is clean.

A new job to check that `go mod tidy` is clean was added, to prevent
easily preventable merge conflicts or go.mod changes being deferred to a
future PR that is unrelated to the change that caused the go.mod to
change.

* More robust caching.

We now cache the go build cache, and the go mod download cache
independently. This is because the download cache contains zips that can
be unpacked in parallel faster than they can be fetched and extracted by
tar. This speeds up the build significantly.

The linter is hostile enough. It does not need to also punish us with
longer build times due to small failures like misspellings.

There are two benefits to doing this:
 - Provide a library function that models can use, reducing code for
   each model implementation
 - Enables a single place to drop in optimized implementations of
   attention based on the backend or other factors. One is provided for
   GGML.

On CUDA this improves token generation rate by about 3%. It does not
have a significant effect on Metal.
Co-authored-by: Daniel Hiltgen <daniel@ollama.com>

We don't need to create and destroy the GGML scheduler for every
context. This introduces extra CPU overhead for every forward
pass and extra memory for contexts that don't actually get scheduled
(for example, KV caches). We can instead just have one scheduler
for the backend and reset it each time we call Compute.

This improves token generation performance by 1-2% and removes
scheduler create/destroy from profile traces.

Currently the following parameters are in the runner but not used:
 - numGPULayers
 - mainGPU
 - threads
 - tensorSplit

This passes them through to the backend, which is where they would
actually get used. However, the GGML backend does not yet do anything
with them.

sapphire rapids has amx support but it ends up having a negative
performance impact.

emerald rapids also has amx support with a positive performance impact
however there's no reasonable way in ggml to differentiate between the
two. the impact is small (~6%) so disable amx entirely for simplicity

This provides integration with the new Ollama engine
(58245413 next ollama runner (#7913)) and the rest of the Ollama
infrastructure such as the runner and Ollama server.

In addition, it also builds out the KV cache infrastructure to
support requirements of how Ollama runs models such as:
 - Parallel processing
 - Memory management for defragmentation and shifting
 - Multi-modal modals

Both old and new engines continue to be supported. By default, only
the old engine is used. To enable the new engine:

Start the server with the OLLAMA_NEW_ENGINE environment variable set:
OLLAMA_NEW_ENGINE=1 ./ollama serve

Start a model that is supported by the Ollama engine. This one is Llama 3.1 8b Q4_K_M:
./ollama run jessegross/llama3.1

We need to sync before retrieving data after async computation.
It is also important to ensure that the Go buffer is not moved by
the GC across function calls so we do a synchronous copy.

Passing in a Go buffer is not safe because the garbage collector could
free or move the memory while the context is still open. However, if
we pass in the size and a nil pointer then GGML will allocate it from
the C side.