A few more forward-declarations, a few less headers. the impact on number of
preprocessed lines for LLVMSupport is negligible (-3K lines) but it's always
good to remove dependencies.
Related discourse thread: https://llvm.discourse.group/t/include-what-you-use-include-cleanup
Looks like e9211e039377 unfortunately broke the sanitizer build bots,
because those bots compile the symbolizer with DLLVM_ENABLE_THREADS=Off.
Likely, before the patch, this header was transitively included.
The cleanup was manual, but assisted by "include-what-you-use". It consists in
1. Removing unused forward declaration. No impact expected.
2. Removing unused headers in .cpp files. No impact expected.
3. Removing unused headers in .h files. This removes implicit dependencies and
is generally considered a good thing, but this may break downstream builds.
I've updated llvm, clang, lld, lldb and mlir deps, and included a list of the
modification in the second part of the commit.
4. Replacing header inclusion by forward declaration. This has the same impact
as 3.
Notable changes:
- llvm/Support/TargetParser.h no longer includes llvm/Support/AArch64TargetParser.h nor llvm/Support/ARMTargetParser.h
- llvm/Support/TypeSize.h no longer includes llvm/Support/WithColor.h
- llvm/Support/YAMLTraits.h no longer includes llvm/Support/Regex.h
- llvm/ADT/SmallVector.h no longer includes llvm/Support/MemAlloc.h nor llvm/Support/ErrorHandling.h
You may need to add some of these headers in your compilation units, if needs be.
As an hint to the impact of the cleanup, running
clang++ -E -Iinclude -I../llvm/include ../llvm/lib/Support/*.cpp -std=c++14 -fno-rtti -fno-exceptions | wc -l
before: 8000919 lines
after: 7917500 lines
Reduced dependencies also helps incremental rebuilds and is more ccache
friendly, something not shown by the above metric :-)
Discourse thread on the topic: https://llvm.discourse.group/t/include-what-you-use-include-cleanup/5831
Currently, compiles with LLVM_ENABLE_THREADS=OFF fail due to this symbol missing. Add it but assert as calling code is (and should be) checking that threading is enabled.
Differential Revision: https://reviews.llvm.org/D116846
This allows to release the QueueLock early and create Thread
independently of the queue processing.
Differential Revision: https://reviews.llvm.org/D115078
On my 96-core cloudtop 'machine', it seems unnecessary to always start
96 threads upfront... particularly as the ThreadPool is created even
with -mlir-disable-threading. Things like the resuling spew in GDB and
the obfuscated output of `(gdb) info threads` are my motivation here,
but it probably also doesn't hurt for at least some efficiency metrics to
avoid creating many threads upfront.
Reviewed By: mehdi_amini
Differential Revision: https://reviews.llvm.org/D115019
This reverts commit 71a7c55f0f021b04b9a7303d0cd391b9161cf303.
The revert broken building llvm-reduce and it is not clear it fixes an
issue with LLVM_ENABLE_THREADS=OFF.
See discussion in https://reviews.llvm.org/D114183 for more details.
This patch adjusts ThreadPool::async to return futures that wrap
the result type of the passed in callable.
To do so, ThreadPool::asyncImpl first creates a shared promise. The
result of the promise is set in a new callable that first executes the
task. The callable is added to the task queue.
Reviewed By: mehdi_amini
Differential Revision: https://reviews.llvm.org/D114183
This adds a new llvm::thread class with the same interface as std::thread
except there is an extra constructor that allows us to set the new thread's
stack size. On Darwin even the default size is boosted to 8MB to match the main
thread.
It also switches all users of the older C-style `llvm_execute_on_thread` API
family over to `llvm::thread` followed by either a `detach` or `join` call and
removes the old API.
Moved definition of DefaultStackSize into the .cpp file to hopefully
fix the build on some (GCC-6?) machines.
This adds a new llvm::thread class with the same interface as std::thread
except there is an extra constructor that allows us to set the new thread's
stack size. On Darwin even the default size is boosted to 8MB to match the main
thread.
It also switches all users of the older C-style `llvm_execute_on_thread` API
family over to `llvm::thread` followed by either a `detach` or `join` call and
removes the old API.
This revision refactors the usage of multithreaded utilities in MLIR to use a common
thread pool within the MLIR context, in addition to a new utility that makes writing
multi-threaded code in MLIR less error prone. Using a unified thread pool brings about
several advantages:
* Better thread usage and more control
We currently use the static llvm threading utilities, which do not allow multiple
levels of asynchronous scheduling (even if there are open threads). This is due to
how the current TaskGroup structure works, which only allows one truly multithreaded
instance at a time. By having our own ThreadPool we gain more control and flexibility
over our job/thread scheduling, and in a followup can enable threading more parts of
the compiler.
* The static nature of TaskGroup causes issues in certain configurations
Due to the static nature of TaskGroup, there have been quite a few problems related to
destruction that have caused several downstream projects to disable threading. See
D104207 for discussion on some related fallout. By having a ThreadPool scoped to
the context, we don't have to worry about destruction and can ensure that any
additional MLIR thread usage ends when the context is destroyed.
Differential Revision: https://reviews.llvm.org/D104516
* Merge QueueLock and CompletionLock.
* Avoid spurious CompletionCondition.notify_all() when ActiveThreads is greater than 0.
* Use default member initializers.
Reviewed By: mehdi_amini
Differential Revision: https://reviews.llvm.org/D78856
The goal of this patch is to maximize CPU utilization on multi-socket or high core count systems, so that parallel computations such as LLD/ThinLTO can use all hardware threads in the system. Before this patch, on Windows, a maximum of 64 hardware threads could be used at most, in some cases dispatched only on one CPU socket.
== Background ==
Windows doesn't have a flat cpu_set_t like Linux. Instead, it projects hardware CPUs (or NUMA nodes) to applications through a concept of "processor groups". A "processor" is the smallest unit of execution on a CPU, that is, an hyper-thread if SMT is active; a core otherwise. There's a limit of 32-bit processors on older 32-bit versions of Windows, which later was raised to 64-processors with 64-bit versions of Windows. This limit comes from the affinity mask, which historically is represented by the sizeof(void*). Consequently, the concept of "processor groups" was introduced for dealing with systems with more than 64 hyper-threads.
By default, the Windows OS assigns only one "processor group" to each starting application, in a round-robin manner. If the application wants to use more processors, it needs to programmatically enable it, by assigning threads to other "processor groups". This also means that affinity cannot cross "processor group" boundaries; one can only specify a "preferred" group on start-up, but the application is free to allocate more groups if it wants to.
This creates a peculiar situation, where newer CPUs like the AMD EPYC 7702P (64-cores, 128-hyperthreads) are projected by the OS as two (2) "processor groups". This means that by default, an application can only use half of the cores. This situation could only get worse in the years to come, as dies with more cores will appear on the market.
== The problem ==
The heavyweight_hardware_concurrency() API was introduced so that only *one hardware thread per core* was used. Once that API returns, that original intention is lost, only the number of threads is retained. Consider a situation, on Windows, where the system has 2 CPU sockets, 18 cores each, each core having 2 hyper-threads, for a total of 72 hyper-threads. Both heavyweight_hardware_concurrency() and hardware_concurrency() currently return 36, because on Windows they are simply wrappers over std:🧵:hardware_concurrency() -- which can only return processors from the current "processor group".
== The changes in this patch ==
To solve this situation, we capture (and retain) the initial intention until the point of usage, through a new ThreadPoolStrategy class. The number of threads to use is deferred as late as possible, until the moment where the std::threads are created (ThreadPool in the case of ThinLTO).
When using hardware_concurrency(), setting ThreadCount to 0 now means to use all the possible hardware CPU (SMT) threads. Providing a ThreadCount above to the maximum number of threads will have no effect, the maximum will be used instead.
The heavyweight_hardware_concurrency() is similar to hardware_concurrency(), except that only one thread per hardware *core* will be used.
When LLVM_ENABLE_THREADS is OFF, the threading APIs will always return 1, to ensure any caller loops will be exercised at least once.
Differential Revision: https://reviews.llvm.org/D71775
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
This is failing to compile when LLVM_ENABLE_THREADS is false,
and the fix is not immediately obvious, so reverting while I look
into it.
llvm-svn: 334658
Previously ThreadPool could only queue async "jobs", i.e. work
that was done for its side effects and not for its result. It's
useful occasionally to queue async work that returns a value.
From an API perspective, this is very intuitive. The previous
API just returned a shared_future<void>, so all we need to do is
make it return a shared_future<T>, where T is the type of value
that the operation returns.
Making this work required a little magic, but ultimately it's not
too bad. Instead of keeping a shared queue<packaged_task<void()>>
we just keep a shared queue<unique_ptr<TaskBase>>, where TaskBase
is a class with a pure virtual execute() method, then have a
templated derived class that stores a packaged_task<T()>. Everything
else works out pretty cleanly.
Differential Revision: https://reviews.llvm.org/D48115
llvm-svn: 334643
But now include a check for CPU_COUNT so we still build on 10 year old
versions of glibc.
Original message:
Use sched_getaffinity instead of std:🧵:hardware_concurrency.
The issue with std:🧵:hardware_concurrency is that it forwards
to libc and some implementations (like glibc) don't take thread
affinity into consideration.
With this change a llvm program that can execute in only 2 cores will
use 2 threads, even if the machine has 32 cores.
This makes benchmarking a lot easier, but should also help if someone
doesn't want to use all cores for compilation for example.
llvm-svn: 314931
Summary:
This reverts D38481. The change breaks systems with older versions of glibc. It
injects a use of CPU_COUNT() from sched.h without checking to ensure that the
function exists first.
Reviewers:
Subscribers:
llvm-svn: 314922
The issue with std:🧵:hardware_concurrency is that it forwards
to libc and some implementations (like glibc) don't take thread
affinity into consideration.
With this change a llvm program that can execute in only 2 cores will
use 2 threads, even if the machine has 32 cores.
This makes benchmarking a lot easier, but should also help if someone
doesn't want to use all cores for compilation for example.
llvm-svn: 314809
By running TSAN on the ThreadPool unit tests it was discovered that the
threads in the pool can pop tasks off the queue at the same time the
"wait" routine is trying to check if the task queue is empty. This patch
fixes this problem by checking for active threads in the waiter before
checking whether the queue is empty.
Patch by Jason Henline.
Differential Revision: http://reviews.llvm.org/D18811
Reviewers: joker.eph, jlebar
llvm-svn: 265618
This is a very simple implementation of a thread pool using C++11
thread. It accepts any std::function<void()> for asynchronous
execution. Individual task can be synchronize using the returned
future, or the client can block on the full queue completion.
In case LLVM is configured with Threading disabled, it falls back
to sequential execution using std::async with launch:deferred.
This is intended to support parallelism for ThinLTO processing in
linker plugin, but is generic enough for any other uses.
This is a recommit of r255444 ; trying to workaround a bug in the
MSVC 2013 standard library. I think I was hit by:
http://connect.microsoft.com/VisualStudio/feedbackdetail/view/791185/std-packaged-task-t-where-t-is-void-or-a-reference-class-are-not-movable
Recommit of r255589, trying to please g++ as well.
Differential Revision: http://reviews.llvm.org/D15464
From: mehdi_amini <mehdi_amini@91177308-0d34-0410-b5e6-96231b3b80d8>
llvm-svn: 255593
This is a very simple implementation of a thread pool using C++11
thread. It accepts any std::function<void()> for asynchronous
execution. Individual task can be synchronize using the returned
future, or the client can block on the full queue completion.
In case LLVM is configured with Threading disabled, it falls back
to sequential execution using std::async with launch:deferred.
This is intended to support parallelism for ThinLTO processing in
linker plugin, but is generic enough for any other uses.
This is a recommit of r255444 ; trying to workaround a bug in the
MSVC 2013 standard library. I think I was hit by:
http://connect.microsoft.com/VisualStudio/feedbackdetail/view/791185/std-packaged-task-t-where-t-is-void-or-a-reference-class-are-not-movable
Differential Revision: http://reviews.llvm.org/D15464
From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 255589
This is a very simple implementation of a thread pool using C++11
thread. It accepts any std::function<void()> for asynchronous
execution. Individual task can be synchronize using the returned
future, or the client can block on the full queue completion.
In case LLVM is configured with Threading disabled, it falls back
to sequential execution using std::async with launch:deferred.
This is intended to support parallelism for ThinLTO processing in
linker plugin, but is generic enough for any other uses.
Differential Revision: http://reviews.llvm.org/D15464
From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 255444
