> -----Original Message----- > From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] > Sent: Tuesday, January 3, 2017 4:32 AM > To: Alex Ng (LIS) <alexng@xxxxxxxxxxxxx> > Cc: devel@xxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; KY > Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; > John Stultz <john.stultz@xxxxxxxxxx>; Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Subject: Re: [PATCH 3/4] hv_util: use do_adjtimex() to update system time > > "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? Yes, that is correct. > > >> > >> 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? This is correct. SYNC flags are sent rarely and usually only after a guest has been resumed from a pause. > > > > >> + > >> + 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. > Agree. A debug level message is reasonable. > > > >> } > >> > >> /* > >> -- > >> 2.9.3 > > -- > Vitaly _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
