diff --git a/CHANGELOG.md b/CHANGELOG.md
index 48b294c1..3f949b64 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,10 @@
 
 ### Changed
 - Split Windows CI test jobs into parallel chunks to avoid timeouts
+- Optimize clock: prioritize EPOCHREALTIME over subprocess-based fallbacks
+- Cache function discovery to avoid duplicate pipeline per test file
+- Reduce subshells in test execution hot path
+- Batch coverage recording with in-memory buffering
 
 ### Fixed
 - JUnit XML report now conforms to the standard schema
diff --git a/src/clock.sh b/src/clock.sh
index d7978559..510040ca 100644
--- a/src/clock.sh
+++ b/src/clock.sh
@@ -8,7 +8,28 @@ function bashunit::clock::_choose_impl() {
   local attempts_count=0
   local attempts
 
-  # 1. Try Perl with Time::HiRes
+  # 1. Try native shell EPOCHREALTIME (fastest - no subprocess, Bash 5.0+)
+  attempts[attempts_count]="EPOCHREALTIME"
+  attempts_count=$((attempts_count + 1))
+  if shell_time="$(bashunit::clock::shell_time)"; then
+    _BASHUNIT_CLOCK_NOW_IMPL="shell"
+    return 0
+  fi
+
+  # 2. Unix date +%s%N (no subprocess overhead on supported systems)
+  attempts[attempts_count]="date"
+  attempts_count=$((attempts_count + 1))
+  if ! bashunit::check_os::is_macos && ! bashunit::check_os::is_alpine; then
+    local result
+    result=$(date +%s%N 2>/dev/null)
+    local _re='^[0-9]+$'
+    if [[ "$result" != *N ]] && [[ "$result" =~ $_re ]]; then
+      _BASHUNIT_CLOCK_NOW_IMPL="date"
+      return 0
+    fi
+  fi
+
+  # 3. Try Perl with Time::HiRes
   attempts[attempts_count]="Perl"
   attempts_count=$((attempts_count + 1))
   if bashunit::dependencies::has_perl && perl -MTime::HiRes -e "" &>/dev/null; then
@@ -16,7 +37,7 @@ function bashunit::clock::_choose_impl() {
     return 0
   fi
 
-  # 2. Try Python 3 with time module
+  # 4. Try Python 3 with time module
   attempts[attempts_count]="Python"
   attempts_count=$((attempts_count + 1))
   if bashunit::dependencies::has_python; then
@@ -24,14 +45,15 @@ function bashunit::clock::_choose_impl() {
     return 0
   fi
 
-  # 3. Try Node.js
+  # 5. Try Node.js
   attempts[attempts_count]="Node"
   attempts_count=$((attempts_count + 1))
   if bashunit::dependencies::has_node; then
     _BASHUNIT_CLOCK_NOW_IMPL="node"
     return 0
   fi
-  # 4. Windows fallback with PowerShell
+
+  # 6. Windows fallback with PowerShell
   attempts[attempts_count]="PowerShell"
   attempts_count=$((attempts_count + 1))
   if bashunit::check_os::is_windows && bashunit::dependencies::has_powershell; then
@@ -39,27 +61,6 @@ function bashunit::clock::_choose_impl() {
     return 0
   fi
 
-  # 5. Unix fallback using `date +%s%N` (if not macOS or Alpine)
-  attempts[attempts_count]="date"
-  attempts_count=$((attempts_count + 1))
-  if ! bashunit::check_os::is_macos && ! bashunit::check_os::is_alpine; then
-    local result
-    result=$(date +%s%N 2>/dev/null)
-    local _re='^[0-9]+$'
-    if [[ "$result" != *N ]] && [[ "$result" =~ $_re ]]; then
-      _BASHUNIT_CLOCK_NOW_IMPL="date"
-      return 0
-    fi
-  fi
-
-  # 6. Try using native shell EPOCHREALTIME (if available)
-  attempts[attempts_count]="EPOCHREALTIME"
-  attempts_count=$((attempts_count + 1))
-  if shell_time="$(bashunit::clock::shell_time)"; then
-    _BASHUNIT_CLOCK_NOW_IMPL="shell"
-    return 0
-  fi
-
   # 7. Very last fallback: seconds resolution only
   attempts[attempts_count]="date-seconds"
   attempts_count=$((attempts_count + 1))
diff --git a/src/coverage.sh b/src/coverage.sh
index 2b06199f..21c51213 100644
--- a/src/coverage.sh
+++ b/src/coverage.sh
@@ -13,6 +13,17 @@ _BASHUNIT_COVERAGE_TRACKED_CACHE_FILE="${_BASHUNIT_COVERAGE_TRACKED_CACHE_FILE:-
 # File to store which tests hit each line (for detailed coverage tooltips)
 _BASHUNIT_COVERAGE_TEST_HITS_FILE="${_BASHUNIT_COVERAGE_TEST_HITS_FILE:-}"
 
+# In-memory buffer for coverage data (reduces file I/O)
+_BASHUNIT_COVERAGE_BUFFER=""
+_BASHUNIT_COVERAGE_BUFFER_COUNT=0
+_BASHUNIT_COVERAGE_BUFFER_LIMIT=100
+_BASHUNIT_COVERAGE_HITS_BUFFER=""
+
+# In-memory caches for hot-path lookups (avoids grep + subshells)
+_BASHUNIT_COVERAGE_TRACK_CACHE=""
+_BASHUNIT_COVERAGE_PATH_CACHE=""
+_BASHUNIT_COVERAGE_IS_PARALLEL=""
+
 # Auto-discover coverage paths from test file names
 # When no explicit coverage paths are set, find source files matching test file base names
 # Example: tests/unit/assert_test.sh -> finds src/assert.sh, src/assert_*.sh
@@ -82,6 +93,14 @@ function bashunit::coverage::init() {
   : >"$_BASHUNIT_COVERAGE_TRACKED_CACHE_FILE"
   : >"$_BASHUNIT_COVERAGE_TEST_HITS_FILE"
 
+  # Reset in-memory caches and buffers
+  _BASHUNIT_COVERAGE_BUFFER=""
+  _BASHUNIT_COVERAGE_BUFFER_COUNT=0
+  _BASHUNIT_COVERAGE_HITS_BUFFER=""
+  _BASHUNIT_COVERAGE_TRACK_CACHE=""
+  _BASHUNIT_COVERAGE_PATH_CACHE=""
+  _BASHUNIT_COVERAGE_IS_PARALLEL=""
+
   export _BASHUNIT_COVERAGE_DATA_FILE
   export _BASHUNIT_COVERAGE_TRACKED_FILES
   export _BASHUNIT_COVERAGE_TRACKED_CACHE_FILE
@@ -105,6 +124,8 @@ function bashunit::coverage::enable_trap() {
 function bashunit::coverage::disable_trap() {
   trap - DEBUG
   set +T
+  # Flush any remaining buffered coverage data
+  bashunit::coverage::flush_buffer
 }
 
 # Normalize file path to absolute
@@ -171,31 +192,86 @@ function bashunit::coverage::record_line() {
   # Skip if coverage data file doesn't exist (trap inherited by child process)
   [[ -z "$_BASHUNIT_COVERAGE_DATA_FILE" ]] && return 0
 
-  # Skip if not tracking this file (uses cache internally)
-  bashunit::coverage::should_track "$file" || return 0
+  # Fast in-memory should_track cache (avoids grep + file I/O per line)
+  case "$_BASHUNIT_COVERAGE_TRACK_CACHE" in
+  *"|${file}:0|"*) return 0 ;;
+  *"|${file}:1|"*) ;;
+  *)
+    # Not cached yet — run full check and cache result
+    if bashunit::coverage::should_track "$file"; then
+      _BASHUNIT_COVERAGE_TRACK_CACHE="${_BASHUNIT_COVERAGE_TRACK_CACHE}|${file}:1|"
+    else
+      _BASHUNIT_COVERAGE_TRACK_CACHE="${_BASHUNIT_COVERAGE_TRACK_CACHE}|${file}:0|"
+      return 0
+    fi
+    ;;
+  esac
 
-  # Normalize file path using cache (must match tracked_files for hit counting)
-  local normalized_file
-  normalized_file=$(bashunit::coverage::normalize_path "$file")
+  # Fast in-memory path normalization cache (avoids cd + pwd subshell per line)
+  local normalized_file=""
+  case "$_BASHUNIT_COVERAGE_PATH_CACHE" in
+  *"|${file}="*)
+    # Extract cached value
+    normalized_file="${_BASHUNIT_COVERAGE_PATH_CACHE#*"|${file}="}"
+    normalized_file="${normalized_file%%"|"*}"
+    ;;
+  *)
+    normalized_file=$(bashunit::coverage::normalize_path "$file")
+    _BASHUNIT_COVERAGE_PATH_CACHE="${_BASHUNIT_COVERAGE_PATH_CACHE}|${file}=${normalized_file}|"
+    ;;
+  esac
 
-  # In parallel mode, use a per-process file to avoid race conditions
+  # Buffer the coverage data in memory
+  _BASHUNIT_COVERAGE_BUFFER="${_BASHUNIT_COVERAGE_BUFFER}${normalized_file}:${lineno}
+"
+  # Also buffer test hit data if in a test context
+  if [[ -n "${_BASHUNIT_COVERAGE_CURRENT_TEST_FILE:-}" && \
+        -n "${_BASHUNIT_COVERAGE_CURRENT_TEST_FN:-}" ]]; then
+    _BASHUNIT_COVERAGE_HITS_BUFFER="${_BASHUNIT_COVERAGE_HITS_BUFFER}${normalized_file}:${lineno}|${_BASHUNIT_COVERAGE_CURRENT_TEST_FILE}:${_BASHUNIT_COVERAGE_CURRENT_TEST_FN}
+"
+  fi
+
+  _BASHUNIT_COVERAGE_BUFFER_COUNT=$((_BASHUNIT_COVERAGE_BUFFER_COUNT + 1))
+
+  # Flush buffer to disk when threshold is reached
+  if [[ $_BASHUNIT_COVERAGE_BUFFER_COUNT -ge \
+        $_BASHUNIT_COVERAGE_BUFFER_LIMIT ]]; then
+    bashunit::coverage::flush_buffer
+  fi
+}
+
+function bashunit::coverage::flush_buffer() {
+  [[ -z "$_BASHUNIT_COVERAGE_BUFFER" ]] && return 0
+
+  # Determine output files (parallel-safe)
   local data_file="$_BASHUNIT_COVERAGE_DATA_FILE"
   local test_hits_file="$_BASHUNIT_COVERAGE_TEST_HITS_FILE"
-  if bashunit::parallel::is_enabled; then
+
+  # Cache the parallel check to avoid function calls
+  if [[ -z "$_BASHUNIT_COVERAGE_IS_PARALLEL" ]]; then
+    if bashunit::parallel::is_enabled; then
+      _BASHUNIT_COVERAGE_IS_PARALLEL="yes"
+    else
+      _BASHUNIT_COVERAGE_IS_PARALLEL="no"
+    fi
+  fi
+
+  if [[ "$_BASHUNIT_COVERAGE_IS_PARALLEL" == "yes" ]]; then
     data_file="${_BASHUNIT_COVERAGE_DATA_FILE}.$$"
     test_hits_file="${_BASHUNIT_COVERAGE_TEST_HITS_FILE}.$$"
   fi
 
-  # Record the hit (only if parent directory exists)
-  if [[ -d "$(dirname "$data_file")" ]]; then
-    echo "${normalized_file}:${lineno}" >>"$data_file"
+  # Write buffered data in a single I/O operation
+  printf '%s' "$_BASHUNIT_COVERAGE_BUFFER" >>"$data_file"
 
-    # Also record which test caused this hit (if we're in a test context)
-    if [[ -n "${_BASHUNIT_COVERAGE_CURRENT_TEST_FILE:-}" && -n "${_BASHUNIT_COVERAGE_CURRENT_TEST_FN:-}" ]]; then
-      # Format: source_file:line|test_file:test_function
-      echo "${normalized_file}:${lineno}|${_BASHUNIT_COVERAGE_CURRENT_TEST_FILE}:${_BASHUNIT_COVERAGE_CURRENT_TEST_FN}" >>"$test_hits_file"
-    fi
+  if [[ -n "$_BASHUNIT_COVERAGE_HITS_BUFFER" ]]; then
+    printf '%s' "$_BASHUNIT_COVERAGE_HITS_BUFFER" >>"$test_hits_file"
   fi
+
+  # Reset buffer
+  _BASHUNIT_COVERAGE_BUFFER=""
+  _BASHUNIT_COVERAGE_HITS_BUFFER=""
+  _BASHUNIT_COVERAGE_BUFFER_COUNT=0
 }
 
 function bashunit::coverage::should_track() {
diff --git a/src/runner.sh b/src/runner.sh
index feabc501..e3ddaea4 100755
--- a/src/runner.sh
+++ b/src/runner.sh
@@ -101,10 +101,15 @@ function bashunit::runner::load_test_files() {
       bashunit::runner::restore_workdir
       continue
     fi
+    local _cached_fns="$functions_for_script"
     if bashunit::parallel::is_enabled; then
-      bashunit::runner::call_test_functions "$test_file" "$filter" "$tag_filter" "$exclude_tag_filter" 2>/dev/null &
+      bashunit::runner::call_test_functions \
+        "$test_file" "$filter" "$tag_filter" \
+        "$exclude_tag_filter" "$_cached_fns" 2>/dev/null &
     else
-      bashunit::runner::call_test_functions "$test_file" "$filter" "$tag_filter" "$exclude_tag_filter"
+      bashunit::runner::call_test_functions \
+        "$test_file" "$filter" "$tag_filter" \
+        "$exclude_tag_filter" "$_cached_fns"
     fi
     bashunit::runner::run_tear_down_after_script "$test_file"
     bashunit::runner::clean_set_up_and_tear_down_after_script
@@ -343,36 +348,48 @@ function bashunit::runner::call_test_functions() {
   local filter="$2"
   local tag_filter="${3:-}"
   local exclude_tag_filter="${4:-}"
+  local cached_functions="${5:-}"
   local IFS=$' \t\n'
-  local prefix="test"
-  # Use cached function names for better performance
-  local filtered_functions
-  filtered_functions=$(bashunit::helper::get_functions_to_run \
-    "$prefix" "$filter" "$_BASHUNIT_CACHED_ALL_FUNCTIONS")
   local -a functions_to_run=()
   local functions_to_run_count=0
-  local _fn
-  while IFS= read -r _fn; do
-    [[ -z "$_fn" ]] && continue
-    functions_to_run[functions_to_run_count]="$_fn"
-    functions_to_run_count=$((functions_to_run_count + 1))
-  done < <(bashunit::runner::functions_for_script "$script" "$filtered_functions")
 
-  # Apply tag filtering if --tag or --exclude-tag was specified
-  if [ -n "$tag_filter" ] || [ -n "$exclude_tag_filter" ]; then
-    local -a tag_filtered=()
-    local tag_filtered_count=0
-    local _tf_fn
-    for _tf_fn in "${functions_to_run[@]+"${functions_to_run[@]}"}"; do
-      local fn_tags
-      fn_tags=$(bashunit::helper::get_tags_for_function "$_tf_fn" "$script")
-      if bashunit::helper::function_matches_tags "$fn_tags" "$tag_filter" "$exclude_tag_filter"; then
-        tag_filtered[tag_filtered_count]="$_tf_fn"
-        tag_filtered_count=$((tag_filtered_count + 1))
-      fi
+  if [[ -n "$cached_functions" ]]; then
+    # Use pre-computed function list from load_test_files (already tag-filtered)
+    local _fn
+    for _fn in $cached_functions; do
+      [[ -z "$_fn" ]] && continue
+      functions_to_run[functions_to_run_count]="$_fn"
+      functions_to_run_count=$((functions_to_run_count + 1))
     done
-    functions_to_run=("${tag_filtered[@]+"${tag_filtered[@]}"}")
-    functions_to_run_count=$tag_filtered_count
+  else
+    # Fallback: compute function list (for direct calls without cache)
+    local prefix="test"
+    local filtered_functions
+    filtered_functions=$(bashunit::helper::get_functions_to_run \
+      "$prefix" "$filter" "$_BASHUNIT_CACHED_ALL_FUNCTIONS")
+    local _fn
+    while IFS= read -r _fn; do
+      [[ -z "$_fn" ]] && continue
+      functions_to_run[functions_to_run_count]="$_fn"
+      functions_to_run_count=$((functions_to_run_count + 1))
+    done < <(bashunit::runner::functions_for_script "$script" "$filtered_functions")
+
+    # Apply tag filtering if --tag or --exclude-tag was specified
+    if [ -n "$tag_filter" ] || [ -n "$exclude_tag_filter" ]; then
+      local -a tag_filtered=()
+      local tag_filtered_count=0
+      local _tf_fn
+      for _tf_fn in "${functions_to_run[@]+"${functions_to_run[@]}"}"; do
+        local fn_tags
+        fn_tags=$(bashunit::helper::get_tags_for_function "$_tf_fn" "$script")
+        if bashunit::helper::function_matches_tags "$fn_tags" "$tag_filter" "$exclude_tag_filter"; then
+          tag_filtered[tag_filtered_count]="$_tf_fn"
+          tag_filtered_count=$((tag_filtered_count + 1))
+        fi
+      done
+      functions_to_run=("${tag_filtered[@]+"${tag_filtered[@]}"}")
+      functions_to_run_count=$tag_filtered_count
+    fi
   fi
 
   if [[ "$functions_to_run_count" -le 0 ]]; then
@@ -541,10 +558,10 @@ function bashunit::runner::run_test() {
   else
     bashunit::state::reset_current_test_interpolated_function_name
   fi
-  local current_assertions_failed="$(bashunit::state::get_assertions_failed)"
-  local current_assertions_snapshot="$(bashunit::state::get_assertions_snapshot)"
-  local current_assertions_incomplete="$(bashunit::state::get_assertions_incomplete)"
-  local current_assertions_skipped="$(bashunit::state::get_assertions_skipped)"
+  local current_assertions_failed="$_BASHUNIT_ASSERTIONS_FAILED"
+  local current_assertions_snapshot="$_BASHUNIT_ASSERTIONS_SNAPSHOT"
+  local current_assertions_incomplete="$_BASHUNIT_ASSERTIONS_INCOMPLETE"
+  local current_assertions_skipped="$_BASHUNIT_ASSERTIONS_SKIPPED"
 
   # (FD = File Descriptor)
   # Duplicate the current std-output (FD 1) and assigns it to FD 3.
@@ -655,8 +672,24 @@ function bashunit::runner::run_test() {
 
   bashunit::runner::parse_result "$fn_name" "$test_execution_result" "$@"
 
-  local total_assertions="$(bashunit::state::calculate_total_assertions "$test_execution_result")"
-  local test_exit_code="$(bashunit::state::get_test_exit_code)"
+  local test_exit_code="$_BASHUNIT_TEST_EXIT_CODE"
+
+  # Extract assertion counts directly via parameter expansion
+  # instead of spawning grep subprocesses
+  local _te_failed="${test_execution_result##*##ASSERTIONS_FAILED=}"
+  _te_failed="${_te_failed%%##*}"
+  local _te_passed="${test_execution_result##*##ASSERTIONS_PASSED=}"
+  _te_passed="${_te_passed%%##*}"
+  local _te_skipped="${test_execution_result##*##ASSERTIONS_SKIPPED=}"
+  _te_skipped="${_te_skipped%%##*}"
+  local _te_incomplete="${test_execution_result##*##ASSERTIONS_INCOMPLETE=}"
+  _te_incomplete="${_te_incomplete%%##*}"
+  local _te_snapshot="${test_execution_result##*##ASSERTIONS_SNAPSHOT=}"
+  _te_snapshot="${_te_snapshot%%##*}"
+  local total_assertions=$(( \
+    ${_te_failed:-0} + ${_te_passed:-0} + ${_te_skipped:-0} + \
+    ${_te_incomplete:-0} + ${_te_snapshot:-0} \
+  ))
 
   local encoded_test_title
   encoded_test_title="${test_execution_result##*##TEST_TITLE=}"
diff --git a/tests/unit/clock_test.sh b/tests/unit/clock_test.sh
index ba94d67a..39f52c70 100644
--- a/tests/unit/clock_test.sh
+++ b/tests/unit/clock_test.sh
@@ -6,6 +6,10 @@ function set_up_before_script() {
   __ORIGINAL_OS=$_BASHUNIT_OS
 }
 
+function set_up() {
+  _BASHUNIT_CLOCK_NOW_IMPL=""
+}
+
 function tear_down_after_script() {
   export _BASHUNIT_OS=$__ORIGINAL_OS
 }
@@ -24,6 +28,7 @@ function mock_date_seconds() {
 
 function test_now_with_perl() {
   bashunit::mock bashunit::clock::shell_time mock_non_existing_fn
+  bashunit::mock date mock_non_existing_fn
   bashunit::mock perl <<<"1720705883457"
   bashunit::mock bashunit::dependencies::has_python mock_false
   bashunit::mock bashunit::dependencies::has_node mock_false
@@ -60,6 +65,7 @@ function test_now_on_windows_without_with_powershell() {
   bashunit::mock bashunit::clock::shell_time mock_non_existing_fn
   bashunit::mock bashunit::dependencies::has_python mock_false
   bashunit::mock bashunit::dependencies::has_node mock_false
+  bashunit::mock date mock_non_existing_fn
 
   assert_same "1727768183281580800" "$(bashunit::clock::now)"
 }
@@ -68,10 +74,10 @@ function test_now_on_windows_without_without_powershell() {
   mock_windows_os
   bashunit::mock bashunit::dependencies::has_perl mock_false
   bashunit::mock bashunit::dependencies::has_powershell mock_false
-  bashunit::mock date <<<"1727768951"
   bashunit::mock bashunit::clock::shell_time mock_non_existing_fn
   bashunit::mock bashunit::dependencies::has_python mock_false
   bashunit::mock bashunit::dependencies::has_node mock_false
+  bashunit::mock date <<<"1727768951"
 
   assert_same "1727768951" "$(bashunit::clock::now)"
 }
@@ -109,16 +115,18 @@ function test_runtime_in_milliseconds_when_not_empty_time() {
   assert_not_empty "$(bashunit::clock::total_runtime_in_milliseconds)"
 }
 
-function test_now_prefers_perl_over_shell_time() {
-  bashunit::mock bashunit::clock::shell_time <<<"1234.0"
+function test_now_prefers_shell_time_over_perl() {
+  bashunit::mock bashunit::clock::shell_time <<<"1234.567890"
   bashunit::mock perl <<<"999999999999"
   bashunit::mock bashunit::dependencies::has_python mock_false
   bashunit::mock bashunit::dependencies::has_node mock_false
 
-  assert_same "999999999999" "$(bashunit::clock::now)"
+  assert_same "1234567890000" "$(bashunit::clock::now)"
 }
 
 function test_now_prefers_python_over_node() {
+  bashunit::mock bashunit::clock::shell_time mock_non_existing_fn
+  bashunit::mock date mock_non_existing_fn
   bashunit::mock perl mock_non_existing_fn
   bashunit::mock bashunit::dependencies::has_python mock_true
   bashunit::mock python <<<"777777777777"
diff --git a/tests/unit/coverage_core_test.sh b/tests/unit/coverage_core_test.sh
index 88c3e80a..73183465 100644
--- a/tests/unit/coverage_core_test.sh
+++ b/tests/unit/coverage_core_test.sh
@@ -185,6 +185,9 @@ function test_coverage_record_line_writes_to_file() {
   bashunit::coverage::record_line "$test_file" "20"
   bashunit::coverage::record_line "$test_file" "10"
 
+  # Flush buffered coverage data to disk before reading
+  bashunit::coverage::flush_buffer
+
   # In parallel mode, data is written to a per-process file
   local data_file="$_BASHUNIT_COVERAGE_DATA_FILE"
   if bashunit::parallel::is_enabled; then