"Alex Ng (LIS)" <alexng@xxxxxxxxxxxxx> writes: >> -----Original Message----- >> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] >> Sent: Monday, January 2, 2017 11:41 AM >> To: devel@xxxxxxxxxxxxxxxxxxxxxx >> Cc: linux-kernel@xxxxxxxxxxxxxxx; KY Srinivasan <kys@xxxxxxxxxxxxx>; >> Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; John Stultz >> <john.stultz@xxxxxxxxxx>; Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Alex Ng >> (LIS) <alexng@xxxxxxxxxxxxx> >> Subject: [PATCH 3/4] hv_util: use do_adjtimex() to update system time >> >> With TimeSync version 4 protocol support we started updating system time >> continuously through the whole lifetime of Hyper-V guests. Every 5 seconds >> there is a time sample from the host which triggers do_settimeofday[64](). >> While the time from the host is very accurate such adjustments may cause >> issues: >> - Time is jumping forward and backward, some applications may misbehave. >> - In case an NTP client is run in parallel things may go south, e.g. when >> an NTP client tries to adjust tick/frequency with ADJ_TICK/ADJ_FREQUENCY >> the Hyper-V module will not see this changes and time will oscillate and >> never converge. >> - Systemd starts annoying you by printing "Time has been changed" every 5 >> seconds to the system log. > > These are all good points. I am working on a patch to address point 2. > It will allow new TimeSync behavior to be disabled even if the TimeSync IC is > enabled from the host. This can be set to prevent TimeSync IC from interfering > with NTP client. > Good, this can happen in parallel to my series, right? >> >> Instead of calling do_settimeofday64() we can pretend being an NTP client >> and use do_adjtimex(). >> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> >> --- >> drivers/hv/hv_util.c | 25 ++++++++++++++++++++++--- >> 1 file changed, 22 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c index >> 94719eb..4c0fbb0 100644 >> --- a/drivers/hv/hv_util.c >> +++ b/drivers/hv/hv_util.c >> @@ -182,9 +182,10 @@ struct adj_time_work { static void >> hv_set_host_time(struct work_struct *work) { >> struct adj_time_work *wrk; >> - s64 host_tns; >> + s64 host_tns, our_tns, delta; >> u64 newtime; >> - struct timespec64 host_ts; >> + struct timespec64 host_ts, our_ts; >> + struct timex txc = {0}; >> >> wrk = container_of(work, struct adj_time_work, work); >> >> @@ -205,7 +206,25 @@ static void hv_set_host_time(struct work_struct >> *work) >> host_tns = (newtime - WLTIMEDELTA) * 100; >> host_ts = ns_to_timespec64(host_tns); >> >> - do_settimeofday64(&host_ts); >> + getnstimeofday64(&our_ts); >> + our_tns = timespec64_to_ns(&our_ts); >> + >> + /* Difference between our time and host time */ >> + delta = host_tns - our_tns; >> + >> + /* Try adjusting time by using phase adjustment if possible */ >> + if (abs(delta) > MAXPHASE) { >> + do_settimeofday64(&host_ts); >> + return; >> + } > > We should also call do_settimeofday64() if the host sends flag > ICTIMESYNCFLAG_SYNC. This is a signal from host that the guest > shall sync with host time immediately (often when the guest has > just booted). Ok, point taken, will do in v2. We don't get ICTIMESYNCFLAG_SYNC very often, right? > >> + >> + txc.modes = ADJ_TICK | ADJ_FREQUENCY | ADJ_OFFSET | >> ADJ_NANO | >> + ADJ_STATUS; >> + txc.tick = TICK_USEC; >> + txc.freq = 0; > > I'm not familiar with the ADJ_FREQUENCY flag. What does setting this to 'zero' achieve? > Are there any side-effects from doing this? Zero means no frequency adjustment required (we reset it in case it was previously made by an NTP client). > >> + txc.status = STA_PLL; >> + txc.offset = delta; >> + do_adjtimex(&txc); > > Might be a good idea to handle the return code from do_adjtimex() and log something > in case of error. I can add a debug message here but as this is a regular action we don't want to get a flood of messages in case this fails permanently. I'd avoid printing info messages here. > >> } >> >> /* >> -- >> 2.9.3 -- Vitaly _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
