diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0858362..db64576 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,6 +12,7 @@ include(flink)
 find_package(elfio QUIET)
 find_package(jsoncpp)
 find_package(Boost COMPONENTS coroutine REQUIRED)
+find_package(absl REQUIRED)
 
 add_subdirectory(softfloat)
 
@@ -104,7 +105,7 @@ if(NOT(DBT_CORE_DEFS STREQUAL DBT_CORE_DEFS-NOTFOUND))
     target_compile_definitions(${PROJECT_NAME} INTERFACE ${DBT_CORE_DEFS})
 endif()
 
-target_link_libraries(${PROJECT_NAME} PUBLIC elfio::elfio softfloat scc-util Boost::coroutine)
+target_link_libraries(${PROJECT_NAME} PUBLIC elfio::elfio softfloat scc-util Boost::coroutine abseil::abseil)
 
 if(TARGET yaml-cpp::yaml-cpp)
     target_compile_definitions(${PROJECT_NAME} PUBLIC WITH_PLUGINS)
diff --git a/src/iss/arch/riscv_hart_common.h b/src/iss/arch/riscv_hart_common.h
index d85a562..e10a647 100644
--- a/src/iss/arch/riscv_hart_common.h
+++ b/src/iss/arch/riscv_hart_common.h
@@ -37,6 +37,7 @@
 
 #include "mstatus.h"
 #include "util/delegate.h"
+#include <absl/container/flat_hash_map.h>
 #include <array>
 #include <cstdint>
 #include <elfio/elfio.hpp>
@@ -259,8 +260,8 @@ template <typename WORD_TYPE> struct priv_if {
     std::function<iss::status(unsigned, WORD_TYPE)> write_csr;
     std::function<iss::status(uint8_t const*)> exec_htif;
     std::function<void(uint16_t, uint16_t, WORD_TYPE)> raise_trap; // trap_id, cause, fault_data
-    std::unordered_map<unsigned, rd_csr_f>& csr_rd_cb;
-    std::unordered_map<unsigned, wr_csr_f>& csr_wr_cb;
+    absl::flat_hash_map<unsigned, rd_csr_f>& csr_rd_cb;
+    absl::flat_hash_map<unsigned, wr_csr_f>& csr_wr_cb;
     hart_state<WORD_TYPE>& state;
     uint8_t& PRIV;
     WORD_TYPE& PC;
@@ -775,7 +776,7 @@ template <typename BASE, typename LOGCAT = logging::disass> struct riscv_hart_co
                                       this->fault_data = fault_data;
                                   },
                               .csr_rd_cb{this->csr_rd_cb},
-                              .csr_wr_cb{csr_wr_cb},
+                              .csr_wr_cb{this->csr_wr_cb},
                               .state{this->state},
                               .PRIV{this->reg.PRIV},
                               .PC{this->reg.PC},
@@ -893,8 +894,8 @@ protected:
     using csr_page_type = typename csr_type::page_type;
     csr_type csr;
 
-    std::unordered_map<unsigned, rd_csr_f> csr_rd_cb;
-    std::unordered_map<unsigned, wr_csr_f> csr_wr_cb;
+    absl::flat_hash_map<unsigned, rd_csr_f> csr_rd_cb;
+    absl::flat_hash_map<unsigned, wr_csr_f> csr_wr_cb;
 
     reg_t mhartid_reg{0x0};
     uint64_t mcycle_csr{0};
diff --git a/src/iss/arch/riscv_hart_m_p.h b/src/iss/arch/riscv_hart_m_p.h
index 8873390..95298bc 100644
--- a/src/iss/arch/riscv_hart_m_p.h
+++ b/src/iss/arch/riscv_hart_m_p.h
@@ -134,7 +134,7 @@ protected:
 
     hart_state<reg_t> state;
 
-    std::unordered_map<uint64_t, uint8_t> atomic_reservation;
+    absl::flat_hash_map<uint64_t, uint8_t> atomic_reservation;
 
     iss::status read_status(unsigned addr, reg_t& val);
     iss::status write_status(unsigned addr, reg_t val);
diff --git a/src/iss/arch/riscv_hart_msu_vp.h b/src/iss/arch/riscv_hart_msu_vp.h
index 1c226c5..ddfe1cb 100644
--- a/src/iss/arch/riscv_hart_msu_vp.h
+++ b/src/iss/arch/riscv_hart_msu_vp.h
@@ -48,9 +48,9 @@
 #ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
 #endif
+#include <fmt/format.h>
 #include <iss/mem/memory_with_htif.h>
 #include <iss/mem/mmu.h>
-#include <fmt/format.h>
 #include <type_traits>
 #include <unordered_map>
 
@@ -150,7 +150,7 @@ protected:
 
     hart_state<reg_t> state;
 
-    std::unordered_map<uint64_t, uint8_t> atomic_reservation;
+    absl::flat_hash_map<uint64_t, uint8_t> atomic_reservation;
 
     iss::status read_status(unsigned addr, reg_t& val);
     iss::status write_status(unsigned addr, reg_t val);
diff --git a/src/iss/arch/riscv_hart_mu_p.h b/src/iss/arch/riscv_hart_mu_p.h
index 6fe9ed7..6166a58 100644
--- a/src/iss/arch/riscv_hart_mu_p.h
+++ b/src/iss/arch/riscv_hart_mu_p.h
@@ -160,7 +160,7 @@ protected:
 
     hart_state<reg_t> state;
 
-    std::unordered_map<uint64_t, uint8_t> atomic_reservation;
+    absl::flat_hash_map<uint64_t, uint8_t> atomic_reservation;
 
     iss::status read_status(unsigned addr, reg_t& val);
     iss::status write_status(unsigned addr, reg_t val);
diff --git a/src/iss/mem/mmu.h b/src/iss/mem/mmu.h
index aedb0a7..60fea1f 100644
--- a/src/iss/mem/mmu.h
+++ b/src/iss/mem/mmu.h
@@ -32,9 +32,9 @@
  *       eyck@minres.com - initial implementation
  ******************************************************************************/
 
-#include "memory_if.h"
 #include "iss/arch/riscv_hart_common.h"
 #include "iss/vm_types.h"
+#include "memory_if.h"
 #include <util/logging.h>
 
 namespace iss {
@@ -238,7 +238,7 @@ private:
 
 protected:
     reg_t satp;
-    std::unordered_map<reg_t, uint64_t> ptw;
+    absl::flat_hash_map<reg_t, uint64_t> ptw;
     std::array<vm_info, 2> vmt;
     std::array<address_type, 4> addr_mode;
 
diff --git a/src/vm/interp/vm_tgc5c.cpp b/src/vm/interp/vm_tgc5c.cpp
index a27706e..a5155e2 100644
--- a/src/vm/interp/vm_tgc5c.cpp
+++ b/src/vm/interp/vm_tgc5c.cpp
@@ -48,7 +48,7 @@
 #include <vector>
 #include <sstream>
 #include <iss/instruction_decoder.h>
-
+#include <absl/container/flat_hash_map.h>
 
 #ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
@@ -262,7 +262,7 @@ private:
     struct translation_buffer {
         std::vector<std::tuple<opcode_e, uint64_t, uint32_t>> entries;
     } tb;
-    std::unordered_map<uint64_t, translation_buffer> tb_lut;
+    absl::flat_hash_map<uint64_t, translation_buffer> tb_lut;
 };
 
 template <typename CODE_WORD> void debug_fn(CODE_WORD insn) {