/** $Id: VBoxServiceTimeSync.cpp 3725 2007-07-19 19:01:52Z vboxsync $ */ /** @file * VBoxService - Guest Additions TimeSync Service. */ /* * Copyright (C) 2007 innotek GmbH * * This file is part of VirtualBox Open Source Edition (OSE), as * available from http://www.virtualbox.org. This file is free software; * you can redistribute it and/or modify it under the terms of the GNU * General Public License as published by the Free Software Foundation, * in version 2 as it comes in the "COPYING" file of the VirtualBox OSE * distribution. VirtualBox OSE is distributed in the hope that it will * be useful, but WITHOUT ANY WARRANTY of any kind. * * If you received this file as part of a commercial VirtualBox * distribution, then only the terms of your commercial VirtualBox * license agreement apply instead of the previous paragraph. */ /** @page pg_vboxservice_timesync The Time Sync Service * * The time sync service plays along with the Time Manager (TM) in the VMM * to keep the guest time accurate using the host machine as reference. * TM will try its best to make sure all timer ticks gets delivered so that * there isn't normally any need to adjust the guest time. * * There are three normal (= acceptable) cases: * -# When the service starts up. This is because ticks and such might * be lost during VM and OS startup. (Need to figure out exactly why!) * -# When the TM is unable to deliver all the ticks and swallows a * backlog of ticks. The threshold for this is configurable with * a default of 60 seconds. * -# The time is adjusted on the host. This can be caused manually by * the user or by some time sync daemon (NTP, LAN server, etc.). * * There are a number of very odd case where adjusting is needed. Here * are some of them: * -# Timer device emulation inaccurancies (like rounding). * -# Inaccurancies in time source VirtualBox uses. * -# The Guest and/or Host OS doesn't perform proper time keeping. This * come about as a result of OS and/or hardware issues. * * The TM is our source for the host time and will make adjustments for * current timer delivery lag. The simplistic approach taken by TM is to * adjust the host time by the current guest timer delivery lag, meaning that * if the guest is behind 1 second with PIT/RTC/++ ticks this should be reflected * in the guest wall time as well. * * Now, there is any amount of trouble we can cause by changing the time. * Most applications probably uses the wall time when they need to measure * things. A walltime that is being juggled about every so often, even if just * a little bit, could occationally upset these measurements by for instance * yielding negative results. * * This bottom line here is that the time sync service isn't really supposed * to do anything and will try avoid having to do anything when possible. * * The implementation uses the latency it takes to query host time as the * absolute maximum precision to avoid messing up under timer tick catchup * and/or heavy host/guest load. (Rational is that a *lot* of stuff may happen * on our way back from ring-3 and TM/VMMDev since we're taking the route * thru the inner EM loop with it's force action processing.) * * But this latency has to be measured from our perspective, which means it * could just as easily come out as 0. (OS/2 and Windows guest only updates * the current time when the timer ticks for instance.) The good thing is * that this isn't really a problem since we won't ever do anything unless * the drift is noticable. * * It now boils down to these three (configuration) factors: * -# g_TimesyncMinAdjust - The minimum drift we will ever bother with. * -# g_TimesyncLatencyFactor - The factor we multiply the latency by to * calculate the dynamic minimum adjust factor. * -# g_TimesyncMaxLatency - When to start discarding the data as utterly * useless and take a rest (someone is too busy to give us good data). */ /******************************************************************************* * Header Files * *******************************************************************************/ #include #include #include #include #include #include #include #include #include #include #include "VBoxServiceInternal.h" /******************************************************************************* * Global Variables * *******************************************************************************/ /** The timesync interval (millseconds). */ uint32_t g_TimeSyncInterval = 0; /** * @see pg_vboxservice_timesync * * @remark OS/2: There is either a 1 second resolution on the DosSetDateTime * API or a but in the settimeofday implementation. Thus, don't * bother unless there is at least a 1 second drift. */ #ifdef RT_OS_OS2 static uint32_t g_TimeSyncMinAdjust = 1000; #else static uint32_t g_TimeSyncMinAdjust = 100; #endif /** @see pg_vboxservice_timesync */ static uint32_t g_TimeSyncLatencyFactor = 8; /** @see pg_vboxservice_timesync */ static uint32_t g_TimeSyncMaxLatency = 250; /** The semaphore we're blocking on. */ static RTSEMEVENTMULTI g_TimeSyncEvent = NIL_RTSEMEVENTMULTI; /** @copydoc VBOXSERVICE::pfnPreInit */ static DECLCALLBACK(int) VBoxServiceTimeSyncPreInit(void) { return VINF_SUCCESS; } /** @copydoc VBOXSERVICE::pfnOption */ static DECLCALLBACK(int) VBoxServiceTimeSyncOption(const char **ppszShort, int argc, char **argv, int *pi) { int rc = -1; if (ppszShort) /* no short options */; else if (!strcmp(argv[*pi], "--timesync-interval")) rc = VBoxServiceArgUInt32(argc, argv, "", pi, &g_TimeSyncInterval, 1, UINT32_MAX - 1); else if (!strcmp(argv[*pi], "--timesync-min-adjust")) rc = VBoxServiceArgUInt32(argc, argv, "", pi, &g_TimeSyncMinAdjust, 0, 3600000); else if (!strcmp(argv[*pi], "--timesync-latency-factor")) rc = VBoxServiceArgUInt32(argc, argv, "", pi, &g_TimeSyncLatencyFactor, 1, 1024); else if (!strcmp(argv[*pi], "--timesync-max-latency")) rc = VBoxServiceArgUInt32(argc, argv, "", pi, &g_TimeSyncMaxLatency, 1, 3600000); return rc; } /** @copydoc VBOXSERVICE::pfnInit */ static DECLCALLBACK(int) VBoxServiceTimeSyncInit(void) { /* * If not specified, find the right interval default. * Then create the event sem to block on. */ if (!g_TimeSyncInterval) g_TimeSyncInterval = g_DefaultInterval * 1000; if (!g_TimeSyncInterval) g_TimeSyncInterval = 10 * 1000; int rc = RTSemEventMultiCreate(&g_TimeSyncEvent); AssertRC(rc); return rc; } /** @copydoc VBOXSERVICE::pfnWorker */ DECLCALLBACK(int) VBoxServiceTimeSyncWorker(bool volatile *pfShutdown) { RTTIME Time; char sz[64]; int rc; unsigned cErrors = 0; for (;;) { /* * Try get a reliable time reading. */ int cTries = 3; do { /* query it. */ RTTIMESPEC GuestNow0, GuestNow, HostNow; RTTimeNow(&GuestNow0); int rc2 = VbglR3GetHostTime(&HostNow); if (RT_FAILURE(rc2)) { if (cErrors++ < 10) VBoxServiceError("VbglR3GetHostTime failed; rc2=%Rrc\n", rc2); break; } RTTimeNow(&GuestNow); /* calc latency and check if it's ok. */ RTTIMESPEC GuestElapsed = GuestNow; RTTimeSpecSub(&GuestElapsed, &GuestNow0); if ((uint32_t)RTTimeSpecGetMilli(&GuestElapsed) < g_TimeSyncMaxLatency) { /* * Calculate the adjustment threshold and the current drift. */ uint32_t MinAdjust = RTTimeSpecGetMilli(&GuestElapsed) * g_TimeSyncLatencyFactor; if (MinAdjust < g_TimeSyncMinAdjust) MinAdjust = g_TimeSyncMinAdjust; RTTIMESPEC Drift = HostNow; RTTimeSpecSub(&Drift, &GuestNow); if (RTTimeSpecGetMilli(&Drift) < 0) MinAdjust += g_TimeSyncMinAdjust; /* extra buffer against moving time backwards. */ RTTIMESPEC AbsDrift = Drift; RTTimeSpecAbsolute(&AbsDrift); if (g_cVerbosity >= 3) { VBoxServiceVerbose(3, "Host: %s (MinAdjust: %RU32 ms)\n", RTTimeToString(RTTimeExplode(&Time, &HostNow), sz, sizeof(sz)), MinAdjust); VBoxServiceVerbose(3, "Guest: - %s => %RDtimespec drift\n", RTTimeToString(RTTimeExplode(&Time, &GuestNow), sz, sizeof(sz)), &Drift); } if (RTTimeSpecGetMilli(&AbsDrift) > MinAdjust) { /* * The drift is to big, we have to make adjustments. :-/ * If we've got adjtime around, try that first - most * *NIX systems have it. Fall back on settimeofday. */ struct timeval tv; #if !defined(RT_OS_OS2) /* PORTME */ RTTimeSpecGetTimeval(Drift, &tv); if (adjtime(&tv, NULL) == 0) { if (g_cVerbosity >= 1) VBoxServiceVerbose(1, "adjtime by %RDtimespec\n", &Drift); cErrors = 0; } else #endif { errno = 0; if (!gettimeofday(&tv, NULL)) { RTTIMESPEC Tmp; RTTimeSpecAdd(RTTimeSpecSetTimeval(&Tmp, &tv), &Drift); if (!settimeofday(RTTimeSpecGetTimeval(&Tmp, &tv), NULL)) { if (g_cVerbosity >= 1) VBoxServiceVerbose(1, "settimeofday to %s\n", RTTimeToString(RTTimeExplode(&Time, &Tmp), sz, sizeof(sz))); #ifdef DEBUG if (g_cVerbosity >= 3) VBoxServiceVerbose(2, " new time %s\n", RTTimeToString(RTTimeExplode(&Time, RTTimeNow(&Tmp)), sz, sizeof(sz))); #endif cErrors = 0; } else if (cErrors++ < 10) VBoxServiceError("settimeofday failed; errno=%d: %s\n", errno, strerror(errno)); } else if (cErrors++ < 10) VBoxServiceError("gettimeofday failed; errno=%d: %s\n", errno, strerror(errno)); } } break; } VBoxServiceVerbose(3, "%RDtimespec: latency too high (%RDtimespec) sleeping 1s\n", GuestElapsed); RTThreadSleep(1000); } while (--cTries > 0); /* * Block for a while. * * The event semaphore takes care of ignoring interruptions and it * allows us to implement service wakeup later. */ if (*pfShutdown) break; int rc2 = RTSemEventMultiWait(g_TimeSyncEvent, g_TimeSyncInterval); if (*pfShutdown) break; if (rc2 != VERR_TIMEOUT && RT_FAILURE(rc2)) { VBoxServiceError("RTSemEventMultiWait failed; rc2=%Rrc\n", rc2); rc = rc2; break; } } RTSemEventMultiDestroy(g_TimeSyncEvent); g_TimeSyncEvent = NIL_RTSEMEVENTMULTI; return rc; } /** @copydoc VBOXSERVICE::pfnStop */ static DECLCALLBACK(void) VBoxServiceTimeSyncStop(void) { RTSemEventMultiSignal(g_TimeSyncEvent); } /** @copydoc VBOXSERVICE::pfnTerm */ static DECLCALLBACK(void) VBoxServiceTimeSyncTerm(void) { RTSemEventMultiDestroy(g_TimeSyncEvent); g_TimeSyncEvent = NIL_RTSEMEVENTMULTI; } /** * The 'timesync' service description. */ VBOXSERVICE g_TimeSync = { /* pszName. */ "timesync", /* pszDescription. */ "Time synchronization", /* pszUsage. */ "[--timesync-interval ] [--timesync-min-adjust ] " "[--timesync-latency-factor ] [--time-sync-max-latency ]" , /* pszOptions. */ " --timesync-interval Specifies the interval at which to synchronize the\n" " time with the host. The default is 10000 ms.\n" " --timesync-min-adjust The minimum absolute drift drift value measured\n" " in milliseconds to make adjustments for.\n" " The default is 1000 ms on OS/2 and 100 ms elsewhere.\n" " --timesync-latency-factor The factor to multiply the time query latency\n" " with to calculate the dynamic minimum adjust time.\n" " The default is 8 times.\n" " --timesync-max-latency The max host timer query latency to accpet.\n" " The default is 250 ms.\n" , /* methods */ VBoxServiceTimeSyncPreInit, VBoxServiceTimeSyncOption, VBoxServiceTimeSyncInit, VBoxServiceTimeSyncWorker, VBoxServiceTimeSyncStop, VBoxServiceTimeSyncTerm };