Allow a `std::unique_ptr` to be moved into the an `IntrusiveRefCntPtr`,
and remove a couple of now-unnecessary `release()` calls.
Differential Revision: https://reviews.llvm.org/D92888
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
Summary:
Reduce include dependencies by no longer including Pass.h from
DataLayout.h. That include seemed irrelevant to DataLayout, as
well as being irrelevant to several users of DataLayout.
Reviewers: rnk
Reviewed By: rnk
Subscribers: mehdi_amini, hiraditya, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D69261
llvm-svn: 375436
Now that we've moved to C++14, we no longer need the llvm::make_unique
implementation from STLExtras.h. This patch is a mechanical replacement
of (hopefully) all the llvm::make_unique instances across the monorepo.
Differential revision: https://reviews.llvm.org/D66259
llvm-svn: 368942
D65628 requires a flag to specify the number of threads for a clang-doc step. It would be good to use ExecutorConcurrency after exposing it instead of creating a new one that has the same purpose.
Differential Revision: https://reviews.llvm.org/D65833
llvm-svn: 368196
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
Summary: We can run the tools on a subset files of compilation database.
Reviewers: ioeric
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D54092
llvm-svn: 346131
Summary:
And add an option to disable this behavior. The option is only used in
AllTUsExecutor to avoid races when running concurrently on multiple
threads.
This fixes PR38869 introduced by r340937.
Reviewers: ioeric, steveire
Reviewed By: ioeric
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D51864
llvm-svn: 341910
Avoid storing duplicated "std::string"s.
clangd's global-symbol-builder takes 20+GB memory running across LLVM
repository. With this patch, the used memory is ~10GB (running on 48
threads, most of meory are AST-related).
Subscribers: klimek, cfe-commits
Differential Revision: https://reviews.llvm.org/D45479
llvm-svn: 329784
Summary:
As result deduplication or reduction is not supported in the framework,
we should leave the deplication to tools (if needed) until the framework supports it.
Reviewers: bkramer
Subscribers: klimek, cfe-commits
Differential Revision: https://reviews.llvm.org/D42111
llvm-svn: 322691
Summary: Tool results are deduplicated by the result key.
Reviewers: hokein
Subscribers: klimek, mgorny, cfe-commits
Differential Revision: https://reviews.llvm.org/D41729
llvm-svn: 321864
Duncan P. N. Exon Smith