Index: perfdata.c
===================================================================
--- perfdata.c	(revision 32915)
+++ perfdata.c	(working copy)
@@ -86,6 +86,73 @@
         LookupAccountSidW(NULL, Sid, szBuffer, &BufferSize, szDomainNameUnused, &DomainNameLen, &Use);
 }
 
+typedef struct _SIDTOUSERNAME
+{
+    LIST_ENTRY List;
+    LPWSTR pszName;
+    ULONG cwcName;
+    BYTE Data[0];
+} SIDTOUSERNAME, *PSIDTOUSERNAME;
+
+static LIST_ENTRY SidToUserNameHead = {&SidToUserNameHead, &SidToUserNameHead};
+
+// CRITICAL_SECTION CGUFSCritSect;
+
+VOID
+WINAPI
+CachedGetUserFromSid(
+    PSID pSid,
+    LPWSTR pUserName,
+    PULONG pcwcUserName)
+{
+    PLIST_ENTRY pCur;
+    PSIDTOUSERNAME pEntry;
+    ULONG cbSid, cwcUserName;
+
+    cwcUserName = *pcwcUserName;
+
+//    EnterCriticalSection(&CGUFSCritSect);
+
+    /* Walk through the list */
+    for(pCur = SidToUserNameHead.Flink;
+        pCur != &SidToUserNameHead;
+        pCur = pCur->Flink)
+    {
+        pEntry = CONTAINING_RECORD(pCur, SIDTOUSERNAME, List);
+        if (EqualSid((PSID)&pEntry->Data, pSid))
+        {
+            wcsncpy(pUserName, pEntry->pszName, cwcUserName);
+            *pcwcUserName = pEntry->cwcName;
+            return;
+        }
+    }
+
+    /* We didn't find the SID in the list, get the name conventional */
+    SidToUserName(pSid, pUserName, cwcUserName);
+
+    /* Allocate a new entry */
+    *pcwcUserName = wcslen(pUserName);
+    cwcUserName = *pcwcUserName + 1;
+    cbSid = GetLengthSid(pSid);
+    pEntry = malloc(sizeof(SIDTOUSERNAME) + cbSid + cwcUserName * sizeof(WCHAR));
+
+    /* Copy the Sid and name to our entry */
+    CopySid(cbSid, (PSID)&pEntry->Data, pSid);
+    pEntry->pszName = (LPWSTR)(pEntry->Data + cbSid);
+    wcsncpy(pEntry->pszName, pUserName, cwcUserName);
+    pEntry->cwcName = cwcUserName;
+
+    /* Insert the new entry */
+    pEntry->List.Flink = &SidToUserNameHead;
+    pEntry->List.Blink = SidToUserNameHead.Blink;
+    SidToUserNameHead.Blink->Flink = &pEntry->List;
+    SidToUserNameHead.Blink = &pEntry->List;
+
+//    LeaveCriticalSection(&CGUFSCritSect);
+
+    return;
+}
+
 void PerfDataRefresh(void)
 {
     SIZE_T                                    ulSize;
@@ -338,7 +405,9 @@
             ZeroMemory(&pPerfData[Idx].IOCounters, sizeof(IO_COUNTERS));
         }
 
-        SidToUserName(ProcessUser, pPerfData[Idx].UserName, sizeof(pPerfData[0].UserName) / sizeof(pPerfData[0].UserName[0]));
+        ULONG cwcUserName = sizeof(pPerfData[0].UserName) / sizeof(pPerfData[0].UserName[0]);
+        CachedGetUserFromSid(ProcessUser, pPerfData[Idx].UserName, &cwcUserName);
+//        SidToUserName(ProcessUser, pPerfData[Idx].UserName, cwcUserName);
 
         if (ProcessSD != NULL)
         {