[compiler-rt] r314877 - [XRay][compiler-rt] Use a hand-written circular buffer in BufferQueue
Dean Michael Berris via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 3 22:20:13 PDT 2017
Author: dberris
Date: Tue Oct 3 22:20:13 2017
New Revision: 314877
URL: http://llvm.org/viewvc/llvm-project?rev=314877&view=rev
Log:
[XRay][compiler-rt] Use a hand-written circular buffer in BufferQueue
Summary:
This change removes the dependency on using a std::deque<...> for the
storage of the buffers in the buffer queue. We instead implement a
fixed-size circular buffer that's resilient to exhaustion, and preserves
the semantics of the BufferQueue.
We're moving away from using std::deque<...> for two reasons:
- We want to remove dependencies on the STL for data structures.
- We want the data structure we use to not require re-allocation in
the normal course of operation.
The internal implementation of the buffer queue uses heap-allocated
arrays that are initialized once when the BufferQueue is created, and
re-uses slots in the buffer array as buffers are returned in order.
We also change the lock used in the implementation to a spinlock
instead of a blocking mutex. We reason that since the release operations
now take very little time in the critical section, that a spinlock would
be appropriate.
This change is related to D38073.
This change is a re-submit with the following changes:
- Keeping track of the live buffers with a counter independent of the
pointers keeping track of the extents of the circular buffer.
- Additional documentation of what the data members are meant to
represent.
Reviewers: dblaikie, kpw, pelikan
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D38119
Modified:
compiler-rt/trunk/lib/xray/xray_buffer_queue.cc
compiler-rt/trunk/lib/xray/xray_buffer_queue.h
compiler-rt/trunk/test/xray/TestCases/Linux/fdr-thread-order.cc
Modified: compiler-rt/trunk/lib/xray/xray_buffer_queue.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_buffer_queue.cc?rev=314877&r1=314876&r2=314877&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_buffer_queue.cc (original)
+++ compiler-rt/trunk/lib/xray/xray_buffer_queue.cc Tue Oct 3 22:20:13 2017
@@ -16,6 +16,7 @@
#include "sanitizer_common/sanitizer_common.h"
#include "sanitizer_common/sanitizer_libc.h"
+#include <algorithm>
#include <cstdlib>
#include <tuple>
@@ -23,18 +24,21 @@ using namespace __xray;
using namespace __sanitizer;
BufferQueue::BufferQueue(std::size_t B, std::size_t N, bool &Success)
- : BufferSize(B), Buffers(N), Mutex(), OwnedBuffers(), Finalizing{0} {
- for (auto &T : Buffers) {
+ : BufferSize(B), Buffers(new std::tuple<Buffer, bool>[N]()),
+ BufferCount(N), Finalizing{0}, OwnedBuffers(new void *[N]()),
+ Next(Buffers.get()), First(Buffers.get()), LiveBuffers(0) {
+ for (size_t i = 0; i < N; ++i) {
+ auto &T = Buffers[i];
void *Tmp = malloc(BufferSize);
if (Tmp == nullptr) {
Success = false;
return;
}
-
auto &Buf = std::get<0>(T);
+ std::get<1>(T) = false;
Buf.Buffer = Tmp;
Buf.Size = B;
- OwnedBuffers.emplace(Tmp);
+ OwnedBuffers[i] = Tmp;
}
Success = true;
}
@@ -42,27 +46,41 @@ BufferQueue::BufferQueue(std::size_t B,
BufferQueue::ErrorCode BufferQueue::getBuffer(Buffer &Buf) {
if (__sanitizer::atomic_load(&Finalizing, __sanitizer::memory_order_acquire))
return ErrorCode::QueueFinalizing;
- __sanitizer::BlockingMutexLock Guard(&Mutex);
- if (Buffers.empty())
+ __sanitizer::SpinMutexLock Guard(&Mutex);
+ if (LiveBuffers == BufferCount)
return ErrorCode::NotEnoughMemory;
- auto &T = Buffers.front();
+
+ auto &T = *Next;
auto &B = std::get<0>(T);
Buf = B;
- B.Buffer = nullptr;
- B.Size = 0;
- Buffers.pop_front();
+ ++LiveBuffers;
+
+ First = Next;
+ if (++Next == (Buffers.get() + BufferCount))
+ Next = Buffers.get();
+
return ErrorCode::Ok;
}
BufferQueue::ErrorCode BufferQueue::releaseBuffer(Buffer &Buf) {
- if (OwnedBuffers.count(Buf.Buffer) == 0)
+ // Blitz through the buffers array to find the buffer.
+ if (std::none_of(OwnedBuffers.get(), OwnedBuffers.get() + BufferCount,
+ [&Buf](void *P) { return P == Buf.Buffer; }))
return ErrorCode::UnrecognizedBuffer;
- __sanitizer::BlockingMutexLock Guard(&Mutex);
+ __sanitizer::SpinMutexLock Guard(&Mutex);
+
+ // This points to a semantic bug, we really ought to not be releasing more
+ // buffers than we actually get.
+ if (LiveBuffers == 0)
+ return ErrorCode::NotEnoughMemory;
// Now that the buffer has been released, we mark it as "used".
- Buffers.emplace(Buffers.end(), Buf, true /* used */);
+ *First = std::make_tuple(Buf, true);
Buf.Buffer = nullptr;
Buf.Size = 0;
+ --LiveBuffers;
+ if (++First == (Buffers.get() + BufferCount))
+ First = Buffers.get();
return ErrorCode::Ok;
}
@@ -74,7 +92,8 @@ BufferQueue::ErrorCode BufferQueue::fina
}
BufferQueue::~BufferQueue() {
- for (auto &T : Buffers) {
+ for (auto I = Buffers.get(), E = Buffers.get() + BufferCount; I != E; ++I) {
+ auto &T = *I;
auto &Buf = std::get<0>(T);
free(Buf.Buffer);
}
Modified: compiler-rt/trunk/lib/xray/xray_buffer_queue.h
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_buffer_queue.h?rev=314877&r1=314876&r2=314877&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_buffer_queue.h (original)
+++ compiler-rt/trunk/lib/xray/xray_buffer_queue.h Tue Oct 3 22:20:13 2017
@@ -17,8 +17,8 @@
#include "sanitizer_common/sanitizer_atomic.h"
#include "sanitizer_common/sanitizer_mutex.h"
-#include <deque>
-#include <unordered_set>
+#include <cstdint>
+#include <memory>
#include <utility>
namespace __xray {
@@ -36,15 +36,30 @@ public:
};
private:
+ // Size of each individual Buffer.
size_t BufferSize;
// We use a bool to indicate whether the Buffer has been used in this
// freelist implementation.
- std::deque<std::tuple<Buffer, bool>> Buffers;
- __sanitizer::BlockingMutex Mutex;
- std::unordered_set<void *> OwnedBuffers;
+ std::unique_ptr<std::tuple<Buffer, bool>[]> Buffers;
+ size_t BufferCount;
+
+ __sanitizer::SpinMutex Mutex;
__sanitizer::atomic_uint8_t Finalizing;
+ // Pointers to buffers managed/owned by the BufferQueue.
+ std::unique_ptr<void *[]> OwnedBuffers;
+
+ // Pointer to the next buffer to be handed out.
+ std::tuple<Buffer, bool> *Next;
+
+ // Pointer to the entry in the array where the next released buffer will be
+ // placed.
+ std::tuple<Buffer, bool> *First;
+
+ // Count of buffers that have been handed out through 'getBuffer'.
+ size_t LiveBuffers;
+
public:
enum class ErrorCode : unsigned {
Ok,
@@ -117,8 +132,9 @@ public:
/// Buffer is marked 'used' (i.e. has been the result of getBuffer(...) and a
/// releaseBuffer(...) operation).
template <class F> void apply(F Fn) {
- __sanitizer::BlockingMutexLock G(&Mutex);
- for (const auto &T : Buffers) {
+ __sanitizer::SpinMutexLock G(&Mutex);
+ for (auto I = Buffers.get(), E = Buffers.get() + BufferCount; I != E; ++I) {
+ const auto &T = *I;
if (std::get<1>(T))
Fn(std::get<0>(T));
}
Modified: compiler-rt/trunk/test/xray/TestCases/Linux/fdr-thread-order.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/test/xray/TestCases/Linux/fdr-thread-order.cc?rev=314877&r1=314876&r2=314877&view=diff
==============================================================================
--- compiler-rt/trunk/test/xray/TestCases/Linux/fdr-thread-order.cc (original)
+++ compiler-rt/trunk/test/xray/TestCases/Linux/fdr-thread-order.cc Tue Oct 3 22:20:13 2017
@@ -1,37 +1,63 @@
// RUN: %clangxx_xray -g -std=c++11 %s -o %t
// RUN: rm fdr-thread-order.* || true
-// RUN: XRAY_OPTIONS="patch_premain=false xray_naive_log=false xray_logfile_base=fdr-thread-order. xray_fdr_log=true verbosity=1 xray_fdr_log_func_duration_threshold_us=0" %run %t 2>&1 | FileCheck %s
-// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t "`ls fdr-thread-order.* | head -1`" | FileCheck %s --check-prefix TRACE
+// RUN: XRAY_OPTIONS="patch_premain=false xray_naive_log=false \
+// RUN: xray_logfile_base=fdr-thread-order. xray_fdr_log=true verbosity=1 \
+// RUN: xray_fdr_log_func_duration_threshold_us=0" %run %t 2>&1 | \
+// RUN: FileCheck %s
+// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t \
+// RUN: "`ls fdr-thread-order.* | head -1`"
+// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t \
+// RUN: "`ls fdr-thread-order.* | head -1`" | \
+// RUN: FileCheck %s --check-prefix TRACE
// RUN: rm fdr-thread-order.*
// FIXME: Make llvm-xray work on non-x86_64 as well.
// REQUIRES: x86_64-linux
// REQUIRES: built-in-llvm-tree
#include "xray/xray_log_interface.h"
-#include <thread>
+#include <atomic>
#include <cassert>
+#include <thread>
constexpr auto kBufferSize = 16384;
constexpr auto kBufferMax = 10;
-thread_local uint64_t var = 0;
-[[clang::xray_always_instrument]] void __attribute__((noinline)) f1() { ++var; }
-[[clang::xray_always_instrument]] void __attribute__((noinline)) f2() { ++var; }
+std::atomic<uint64_t> var{0};
+
+[[clang::xray_always_instrument]] void __attribute__((noinline)) f1() {
+ for (auto i = 0; i < 1 << 20; ++i)
+ ++var;
+}
+
+[[clang::xray_always_instrument]] void __attribute__((noinline)) f2() {
+ for (auto i = 0; i < 1 << 20; ++i)
+ ++var;
+}
int main(int argc, char *argv[]) {
using namespace __xray;
FDRLoggingOptions Options;
+ __xray_patch();
assert(__xray_log_init(kBufferSize, kBufferMax, &Options,
sizeof(FDRLoggingOptions)) ==
XRayLogInitStatus::XRAY_LOG_INITIALIZED);
- __xray_patch();
- std::thread t1([] { f1(); });
- std::thread t2([] { f2(); });
- t1.join();
- t2.join();
+
+ std::atomic_thread_fence(std::memory_order_acq_rel);
+
+ {
+ std::thread t1([] { f1(); });
+ std::thread t2([] { f2(); });
+ t1.join();
+ t2.join();
+ }
+
+ std::atomic_thread_fence(std::memory_order_acq_rel);
__xray_log_finalize();
__xray_log_flushLog();
+ __xray_unpatch();
+ return var > 0 ? 0 : 1;
// CHECK: {{.*}}XRay: Log file in '{{.*}}'
+ // CHECK-NOT: Failed
}
// We want to make sure that the order of the function log doesn't matter.
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