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Change default thread pool sizes to respect processor affinity (#6604)

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Instead of using the number of processors in the host, use the number of
processors available to the process, respecting cpu affinity
assignments. Without pthreads, fall back and use the number of
processors in the host as before.

This is now applied everywhere so runing `nuamctl -C 0-3 verilator` or
`numactl -C 0-3 Vsim` should behave as if the host has 4 cores (e.g.
like in CI jobs)
This commit is contained in:
Geza Lore
2025-10-28 18:10:40 +00:00
committed by GitHub
parent 5642de432b
commit ffbb3229a8
12 changed files with 72 additions and 45 deletions
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include/verilated_threads.cpp
+8 -20
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@@ -118,30 +118,18 @@ VlThreadPool::~VlThreadPool() {
for (auto& i : m_workers) delete i;
}
bool VlThreadPool::isNumactlRunning() {
// We assume if current thread is CPU-masked, then under numactl, otherwise not.
// This shows that numactl is visible through the affinity mask
#if defined(__linux) || defined(CPU_ZERO) // Linux-like; assume we have pthreads etc
const unsigned num_cpus = std::thread::hardware_concurrency();
cpu_set_t cpuset;
CPU_ZERO(&cpuset);
const int rc = pthread_getaffinity_np(pthread_self(), sizeof(cpu_set_t), &cpuset);
if (rc != 0) return true; // Error; assuming returning true is the least-damage option
for (unsigned c = 0; c < std::min(num_cpus, static_cast<unsigned>(CPU_SETSIZE)); ++c) {
if (!CPU_ISSET(c, &cpuset)) return true;
}
#endif
return false;
}
std::string VlThreadPool::numaAssign() {
#if defined(__linux) || defined(CPU_ZERO) || defined(VL_CPPCHECK) // Linux-like pthreads
// If not under numactl, make a reasonable processor affinity selection
if (isNumactlRunning()) return "running under numactl"; // User presumably set affinity
// Get number of processor available to the current process
const unsigned num_proc = VlOs::getProcessAvailableParallelism();
if (!num_proc) return "Can't determine number of available threads";
// If fewer than hardware threads in the host, user presumably set affinity
if (num_proc < std::thread::hardware_concurrency()) return "processor affinity already set";
// Make a reasonable processor affinity selection
const int num_threads = static_cast<int>(m_workers.size());
const int num_proc = static_cast<int>(std::thread::hardware_concurrency());
if (num_threads < 2) return "too few threads";
if (num_threads > num_proc) return "too many threads";
if (static_cast<unsigned>(num_threads) > num_proc) return "too many threads";
// Read CPU info.
// Uncertain if any modern system has gaps in the processor id (Solaris