mirror of
https://github.com/cirosantilli/linux-kernel-module-cheat.git
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111 lines
3.0 KiB
C++
111 lines
3.0 KiB
C++
// https://cirosantilli.com/linux-kernel-module-cheat#atomic-cpp
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#if __cplusplus >= 201103L
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#include <atomic>
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#include <cassert>
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#include <iostream>
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#include <mutex>
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#include <thread>
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#include <vector>
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size_t niters;
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#if LKMC_USERLAND_ATOMIC_STD_ATOMIC
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std::atomic_ulong global(0);
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#else
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uint64_t global = 0;
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#endif
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#if LKMC_USERLAND_ATOMIC_MUTEX
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std::mutex mutex;
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#endif
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void threadMain() {
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for (size_t i = 0; i < niters; ++i) {
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#if LKMC_USERLAND_ATOMIC_MUTEX
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mutex.lock();
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#endif
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#if LKMC_USERLAND_ATOMIC_X86_64_INC
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__asm__ __volatile__ (
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"incq %0;"
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: "+g" (global),
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"+g" (i) // to prevent loop unrolling, and make results more comparable across methods,
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// see also: https://cirosantilli.com/linux-kernel-module-cheat#infinite-busy-loop
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:
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:
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);
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#elif LKMC_USERLAND_ATOMIC_X86_64_LOCK_INC
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// https://cirosantilli.com/linux-kernel-module-cheat#x86-lock-prefix
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__asm__ __volatile__ (
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"lock incq %0;"
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: "+m" (global),
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"+g" (i) // to prevent loop unrolling
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:
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:
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);
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#elif LKMC_USERLAND_ATOMIC_AARCH64_ADD
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__asm__ __volatile__ (
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"add %0, %0, 1;"
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: "+r" (global),
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"+g" (i) // to prevent loop unrolling
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:
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:
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);
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#elif LKMC_USERLAND_ATOMIC_AARCH64_LDADD
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// https://cirosantilli.com/linux-kernel-module-cheat#arm-lse
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__asm__ __volatile__ (
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"ldadd %[inc], xzr, [%[addr]];"
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: "=m" (global),
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"+g" (i) // to prevent loop unrolling
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: [inc] "r" (1),
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[addr] "r" (&global)
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:
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);
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#else
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__asm__ __volatile__ (
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""
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: "+g" (i) // to prevent he loop from being optimized to a single add
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// see also: https://stackoverflow.com/questions/37786547/enforcing-statement-order-in-c/56865717#56865717
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: "g" (global)
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:
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);
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global++;
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#endif
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#if LKMC_USERLAND_ATOMIC_MUTEX
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mutex.unlock();
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#endif
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}
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}
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#endif
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int main(int argc, char **argv) {
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#if __cplusplus >= 201103L
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size_t nthreads;
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if (argc > 1) {
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nthreads = std::stoull(argv[1], NULL, 0);
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} else {
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nthreads = 2;
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}
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if (argc > 2) {
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niters = std::stoull(argv[2], NULL, 0);
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} else {
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niters = 10;
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}
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std::vector<std::thread> threads(nthreads);
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for (size_t i = 0; i < nthreads; ++i)
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threads[i] = std::thread(threadMain);
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for (size_t i = 0; i < nthreads; ++i)
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threads[i].join();
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uint64_t expect = nthreads * niters;
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#if LKMC_USERLAND_ATOMIC_FAIL || \
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LKMC_USERLAND_ATOMIC_X86_64_INC || \
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LKMC_USERLAND_ATOMIC_AARCH64_INC
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// These fail, so we just print the outcomes.
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std::cout << "expect " << expect << std::endl;
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std::cout << "global " << global << std::endl;
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#else
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assert(global == expect);
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#endif
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#endif
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}
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