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Remap thread id to avoid bitmap contention #223

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Remap thread id to avoid bitmap contention #223

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4bfccf5
v0
Jun 10, 2025
a9eda77
Remove unnecessary import
Jun 10, 2025
cc95793
Rename
Jun 11, 2025
bb2a116
Added assertion for potential mapped thread id overflow
Jun 11, 2025
a3d2477
Reverse lower 16 bits, instead of swapping lower 2 bytes
zhengyu123 Jun 12, 2025
0b128b5
jbachorik's comment
zhengyu123 Jun 16, 2025
463e8eb
Sign the patch
zhengyu123 Jun 17, 2025
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Reverse lower 16 bits, instead of swapping lower 2 bytes
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@zhengyu123
zhengyu123 committed Jun 12, 2025
commit a3d2477d439f2c865e29fe46a956a7ad4a283d43
23 changes: 23 additions & 0 deletions ddprof-lib/src/main/cpp/reverse_bits.h
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Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
//
// Borrow the implementation from openjdk
// https://github.com/openjdk/jdk/blob/master/src/hotspot/share/utilities/reverse_bits.hpp
//

#ifndef REVERSE_BITS_H
#define REVERSE_BITS_H
#include "arch_dd.h"
#include <stdint.h>

static constexpr u32 rep_5555 = static_cast<u32>(UINT64_C(0x5555555555555555));
static constexpr u32 rep_3333 = static_cast<u32>(UINT64_C(0x3333333333333333));
static constexpr u32 rep_0F0F = static_cast<u32>(UINT64_C(0x0F0F0F0F0F0F0F0F));

inline u16 reverse16(u16 v) {
u32 x = static_cast<u32>(v);
x = ((x & rep_5555) << 1) | ((x >> 1) & rep_5555);
x = ((x & rep_3333) << 2) | ((x >> 2) & rep_3333);
x = ((x & rep_0F0F) << 4) | ((x >> 4) & rep_0F0F);
return __builtin_bswap16(static_cast<u16>(x));
}

#endif //REVERSE_BITS_H
3 changes: 2 additions & 1 deletion ddprof-lib/src/main/cpp/threadFilter.cpp
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Expand Up @@ -17,6 +17,7 @@
#include "threadFilter.h"
#include "counters.h"
#include "os.h"
#include "reverse_bits.h"
#include <stdlib.h>
#include <string.h>

Expand Down Expand Up @@ -89,7 +90,7 @@ int ThreadFilter::mapThreadId(int thread_id) {
// We want to map the thread_id inside the same bitmap
static_assert(BITMAP_SIZE >= (u16)0xffff, "Potential verflow");
u16 lower16 = (u16)(thread_id & 0xffff);
lower16 = ((lower16 & 0x00ff) << 8) | ((lower16 & 0xff00) >> 8);
lower16 = reverse16(lower16);
int tid = (thread_id & ~0xffff) | lower16;
return tid;
}
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