diff --git a/cista/protocol.py b/cista/protocol.py
index 6714f39..da76018 100644
--- a/cista/protocol.py
+++ b/cista/protocol.py
@@ -112,7 +112,7 @@ class ErrorMsg(msgspec.Struct):
 ## Directory listings
 
 
-class FileEntry(msgspec.Struct, array_like=True):
+class FileEntry(msgspec.Struct, array_like=True, frozen=True):
     level: int
     name: str
     key: str
diff --git a/cista/watching.py b/cista/watching.py
index a74d0c8..47d2c22 100644
--- a/cista/watching.py
+++ b/cista/watching.py
@@ -46,87 +46,70 @@ class State:
         with self.lock:
             self._listing = listing
 
-    def _slice(self, idx: PurePosixPath | tuple[PurePosixPath, int]):
-        relpath, relfile = idx if isinstance(idx, tuple) else (idx, 0)
-        begin, end = 0, len(self._listing)
-        level = 0
-        isfile = 0
 
-        # Special case for root
-        if not relpath.parts:
-            return slice(begin, end)
+def treeiter(rootmod):
+    relpath = PurePosixPath()
+    for i, entry in enumerate(rootmod):
+        if entry.level > 0:
+            relpath = PurePosixPath(*relpath.parts[: entry.level - 1]) / entry.name
+        yield i, relpath, entry
 
-        for part in relpath.parts:
+
+def treeget(rootmod: list[FileEntry], path: PurePosixPath):
+    begin = None
+    ret = []
+    for i, relpath, entry in treeiter(rootmod):
+        if begin is None:
+            if relpath == path:
+                begin = i
+                ret.append(entry)
+            continue
+        if entry.level <= len(path.parts):
+            break
+        ret.append(entry)
+    return begin, ret
+
+
+def treeinspos(rootmod: list[FileEntry], relpath: PurePosixPath, relfile: int):
+    # Find the first entry greater than the new one
+    # precondition: the new entry doesn't exist
+    isfile = 0
+    level = 0
+    i = 0
+    for i, rel, entry in treeiter(rootmod):
+        if entry.level > level:
+            # We haven't found item at level, skip subdirectories
+            continue
+        if entry.level < level:
+            # We have passed the level, so the new item is the first
+            return i
+        if level == 0:
+            # root
             level += 1
-            found = False
-
-            # Traverse contents of a folder at level
-            while begin + 1 < end:
-                begin += 1
-                entry = self._listing[begin]
-
-                # Skip subentries
-                if entry.level > level:
-                    continue
-
-                # The directory we were traversing has ended
-                if entry.level < level:
-                    break
-
-                # Found the requested part?
-                if entry.name == part:
-                    found = True
-                    # Are we finished yet?
-                    if level == len(relpath.parts):
-                        isfile = relfile
-                    else:
-                        # Enter subdirectory
-                        continue
-                    break
-
-                # Checking if past the requested spot in sort order
-                cmp = entry.isfile - isfile or sortkey(entry.name) > sortkey(part)
-                if cmp > 0:
-                    break
-
-            if not found:
-                if level < len(relpath.parts) - 1:
-                    # Fail if the parent folder is missing
-                    parent = "/".join(relpath.parts[:level])
-                    raise ValueError(
-                        f"Parent folder {parent} is missing for {relpath.as_posix()} at {level=}"
-                    )
-                # Insertion point at the end of the directory
-                return slice(begin, begin)
-
-            # Otherwise found=True, continue to the next part if not there yet
-
-        # Found the starting point, now find the end of the slice
-        for end in range(begin + 1, len(self._listing) + 1):
-            if end == len(self._listing) or self._listing[end].level <= level:
-                break
-        return slice(begin, end)
-
-    def __getitem__(self, index: PurePosixPath | tuple[PurePosixPath, int]):
-        with self.lock:
-            return self._listing[self._slice(index)]
-
-    def __setitem__(
-        self, index: tuple[PurePosixPath, int], value: list[FileEntry]
-    ) -> None:
-        rel, isfile = index
-        with self.lock:
-            if rel.parts:
-                parent = self._slice(rel.parent)
-                if parent.start == parent.stop:
-                    raise ValueError(
-                        f"Parent folder {rel.as_posix()} is missing for {rel.name} {level=}"
-                    )
-            self._listing[self._slice(index)] = value
-
-    def __delitem__(self, relpath: PurePosixPath):
-        with self.lock:
-            del self._listing[self._slice(relpath)]
+            continue
+        ename = rel.parts[level - 1]
+        name = relpath.parts[level - 1]
+        esort = sortkey(ename)
+        nsort = sortkey(name)
+        # Non-leaf are always folders, only use relfile at leaf
+        isfile = relfile if len(relpath.parts) == level else 0
+        # First compare by isfile, then by sorting order and if that too matches then case sensitive
+        cmp = (
+            entry.isfile - isfile
+            or (esort > nsort) - (esort < nsort)
+            or (ename > name) - (ename < name)
+        )
+        if cmp > 0:
+            return i
+        if cmp < 0:
+            continue
+        level += 1
+        if level > len(relpath.parts):
+            print("ERROR: insertpos", relpath, i, entry.name, entry.level, level)
+            break
+    else:
+        i += 1
+    return i
 
 
 state = State()
@@ -141,7 +124,7 @@ def walk(rel: PurePosixPath, stat: stat_result | None = None) -> list[FileEntry]
     ret = []
     try:
         st = stat or path.stat()
-        isfile = not S_ISDIR(st.st_mode)
+        isfile = int(not S_ISDIR(st.st_mode))
         entry = FileEntry(
             level=len(rel.parts),
             name=rel.name,
@@ -170,10 +153,17 @@ def walk(rel: PurePosixPath, stat: stat_result | None = None) -> list[FileEntry]
         # Build the tree as a list of FileEntries
         for [_, name, s] in humansorted(li):
             sub = walk(rel / name, stat=s)
-            ret.extend(sub)
             child = sub[0]
-            entry.mtime = max(entry.mtime, child.mtime)
-            entry.size += child.size
+            entry = FileEntry(
+                entry.level,
+                entry.name,
+                entry.key,
+                entry.size + child.size,
+                max(entry.mtime, child.mtime),
+                entry.isfile,
+            )
+            ret[0] = entry
+            ret.extend(sub)
     except FileNotFoundError:
         pass  # Things may be rapidly in motion
     except OSError as e:
@@ -193,23 +183,25 @@ def update_root(loop):
             broadcast(format_update(old, new), loop)
 
 
-def update_path(relpath: PurePosixPath, loop):
+def update_path(rootmod: list[FileEntry], relpath: PurePosixPath, loop):
     """Called on FS updates, check the filesystem and broadcast any changes."""
     new = walk(relpath)
-    with state.lock:
-        old = state[relpath]
-        if old == new:
-            return
-        old = state.root
-        if new:
-            logger.debug(
-                f"Watch: Update {relpath}" if old else f"Watch: Created {relpath}"
-            )
-            state[relpath, new[0].isfile] = new
-        else:
-            logger.debug(f"Watch: Removed {relpath}")
-            del state[relpath]
-        broadcast(format_update(old, state.root), loop)
+    obegin, old = treeget(rootmod, relpath)
+    if old == new:
+        logger.debug(
+            f"Watch: Event without changes needed {relpath}"
+            if old
+            else f"Watch: Event with old and new missing: {relpath}"
+        )
+        return
+    if obegin is not None:
+        del rootmod[obegin : obegin + len(old)]
+    if new:
+        logger.debug(f"Watch: Update {relpath}" if old else f"Watch: Created {relpath}")
+        i = treeinspos(rootmod, relpath, new[0].isfile)
+        rootmod[i:i] = new
+    else:
+        logger.debug(f"Watch: Removed {relpath}")
 
 
 def update_space(loop):
@@ -231,40 +223,57 @@ def update_space(loop):
 def format_update(old, new):
     # Make keep/del/insert diff until one of the lists ends
     oidx, nidx = 0, 0
+    oremain, nremain = set(old), set(new)
     update = []
     keep_count = 0
     while oidx < len(old) and nidx < len(new):
+        modified = False
+        # Matching entries are kept
         if old[oidx] == new[nidx]:
+            entry = old[oidx]
+            oremain.remove(entry)
+            nremain.remove(entry)
             keep_count += 1
             oidx += 1
             nidx += 1
             continue
         if keep_count > 0:
+            modified = True
             update.append(UpdKeep(keep_count))
             keep_count = 0
 
+        # Items only in old are deleted
         del_count = 0
-        rest = new[nidx:]
-        while oidx < len(old) and old[oidx] not in rest:
+        while oidx < len(old) and old[oidx] not in nremain:
+            oremain.remove(old[oidx])
             del_count += 1
             oidx += 1
         if del_count:
             update.append(UpdDel(del_count))
             continue
 
+        # Items only in new are inserted
         insert_items = []
-        rest = old[oidx:]
-        while nidx < len(new) and new[nidx] not in rest:
-            insert_items.append(new[nidx])
+        while nidx < len(new) and new[nidx] not in oremain:
+            entry = new[nidx]
+            nremain.remove(entry)
+            insert_items.append(entry)
             nidx += 1
-        update.append(UpdIns(insert_items))
+        if insert_items:
+            modified = True
+            update.append(UpdIns(insert_items))
+
+        if not modified:
+            raise Exception(
+                f"Infinite loop in diff {nidx=} {oidx=} {len(old)=} {len(new)=}"
+            )
 
     # Diff any remaining
     if keep_count > 0:
         update.append(UpdKeep(keep_count))
-    if oidx < len(old):
-        update.append(UpdDel(len(old) - oidx))
-    elif nidx < len(new):
+    if oremain:
+        update.append(UpdDel(len(oremain)))
+    elif nremain:
         update.append(UpdIns(new[nidx:]))
 
     return msgspec.json.encode({"update": update}).decode()
@@ -310,13 +319,14 @@ def watcher_inotify(loop):
     while not quit.is_set():
         i = inotify.adapters.InotifyTree(rootpath.as_posix())
         # Initialize the tree from filesystem
+        t0 = time.perf_counter()
         update_root(loop)
+        t1 = time.perf_counter()
+        logger.debug(f"Root update took {t1 - t0:.1f}s")
         trefresh = time.monotonic() + 30.0
         tspace = time.monotonic() + 5.0
         # Watch for changes (frequent wakeups needed for quiting)
-        for event in i.event_gen(timeout_s=0.1):
-            if quit.is_set():
-                break
+        while not quit.is_set():
             t = time.monotonic()
             # The watching is not entirely reliable, so do a full refresh every 30 seconds
             if t >= trefresh:
@@ -325,11 +335,34 @@ def watcher_inotify(loop):
             if t >= tspace:
                 tspace = time.monotonic() + 5.0
                 update_space(loop)
-            # Inotify event, update the tree
-            if event and any(f in modified_flags for f in event[1]):
-                # Update modified path
-                path = PurePosixPath(event[2]) / event[3]
-                update_path(path.relative_to(rootpath), loop)
+            # Inotify events, update the tree
+            events = list(i.event_gen(yield_nones=False, timeout_s=0.1))
+            dirty = False
+            rootmod = list(state.root)
+            for event in events:
+                assert event
+                interesting = any(f in modified_flags for f in event[1])
+                if event[2] == rootpath.as_posix() and event[3] == "zzz":
+                    logger.debug(f"Watch: {interesting=} {event=}")
+                if interesting:
+                    # Update modified path
+                    t0 = time.perf_counter()
+                    path = PurePosixPath(event[2]) / event[3]
+                    update_path(rootmod, path.relative_to(rootpath), loop)
+                    t1 = time.perf_counter()
+                    logger.debug(f"Watch: Update {event[3]} took {t1 - t0:.1f}s")
+                    dirty = True
+            if dirty and state.root != rootmod:
+                t0 = time.perf_counter()
+                update = format_update(state.root, rootmod)
+                t1 = time.perf_counter()
+                with state.lock:
+                    broadcast(update, loop)
+                    state.root = rootmod
+                t2 = time.perf_counter()
+                logger.debug(
+                    f"Format update took {t1 - t0:.1f}s, broadcast {t2 - t1:.1f}s"
+                )
 
         del i  # Free the inotify object
 
diff --git a/tests/test_watching.py b/tests/test_watching.py
index 81301a7..c358469 100644
--- a/tests/test_watching.py
+++ b/tests/test_watching.py
@@ -1,10 +1,7 @@
-from pathlib import PurePosixPath
-
 import msgspec
-import pytest
 
 from cista.protocol import FileEntry, UpdateMessage, UpdDel, UpdIns, UpdKeep
-from cista.watching import State, format_update
+from cista.watching import format_update
 
 
 def decode(data: str):
@@ -37,6 +34,14 @@ def test_insertions():
     assert decode(format_update(old_list, new_list)) == expected
 
 
+def test_insertion_at_end():
+    old_list = [*f(3), FileEntry(1, "xxx", "xxx", 0, 0, 1)]
+    newfile = FileEntry(1, "yyy", "yyy", 0, 0, 1)
+    new_list = [*old_list, newfile]
+    expected = [UpdKeep(4), UpdIns([newfile])]
+    assert decode(format_update(old_list, new_list)) == expected
+
+
 def test_deletions():
     old_list = f(3)
     new_list = [old_list[0], old_list[2]]
@@ -83,54 +88,3 @@ def test_longer_lists():
 def sortkey(name):
     # Define the sorting key for names here
     return name.lower()
-
-
-@pytest.fixture()
-def state():
-    entries = [
-        FileEntry(0, "", "root", 0, 0, 0),
-        FileEntry(1, "bar", "bar", 0, 0, 0),
-        FileEntry(2, "baz", "bar/baz", 0, 0, 0),
-        FileEntry(1, "foo", "foo", 0, 0, 0),
-        FileEntry(1, "xxx", "xxx", 0, 0, 0),
-        FileEntry(2, "yyy", "xxx/yyy", 0, 0, 1),
-    ]
-    s = State()
-    s._listing = entries
-    return s
-
-
-def test_existing_directory(state):
-    path = PurePosixPath("bar")
-    expected_slice = slice(1, 3)  # Includes 'bar' and 'baz'
-    assert state._slice(path) == expected_slice
-
-
-def test_existing_file(state):
-    path = PurePosixPath("xxx/yyy")
-    expected_slice = slice(5, 6)  # Only includes 'yyy'
-    assert state._slice(path) == expected_slice
-
-
-def test_nonexistent_directory(state):
-    path = PurePosixPath("zzz")
-    expected_slice = slice(6, 6)  # 'zzz' would be inserted at end
-    assert state._slice(path) == expected_slice
-
-
-def test_nonexistent_file(state):
-    path = (PurePosixPath("bar/mmm"), 1)
-    expected_slice = slice(3, 3)  # A file would be inserted after 'baz' under 'bar'
-    assert state._slice(path) == expected_slice
-
-
-def test_root_directory(state):
-    path = PurePosixPath()
-    expected_slice = slice(0, 6)  # Entire tree
-    assert state._slice(path) == expected_slice
-
-
-def test_directory_with_subdirs_and_files(state):
-    path = PurePosixPath("xxx")
-    expected_slice = slice(4, 6)  # Includes 'xxx' and 'yyy'
-    assert state._slice(path) == expected_slice