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Re: [PATCH v2 4/4] hv_util: improve time adjustment accuracy by disabling interrupts

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John Stultz <john.stultz@linaro.org> writes:

> On Wed, Jan 4, 2017 at 9:24 AM, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>> If we happen to receive interrupts during hv_set_host_time() execution
>> our adjustments may get inaccurate. Make the whole function atomic.
>> Unfortunately, we can's call do_settimeofday64() with interrupts
>> disabled as some cross-CPU work is being done but this call happens
>> very rarely.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  drivers/hv/hv_util.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
>> index 7e97231..4e50a42 100644
>> --- a/drivers/hv/hv_util.c
>> +++ b/drivers/hv/hv_util.c
>> @@ -187,6 +187,9 @@ static void hv_set_host_time(struct work_struct *work)
>>         struct timespec64 host_ts, our_ts;
>>         struct timex txc = {0};
>>         int ret;
>> +       unsigned long flags;
>> +
>> +       local_irq_save(flags);
>>
>>         wrk = container_of(work, struct adj_time_work, work);
>>
>> @@ -218,6 +221,7 @@ static void hv_set_host_time(struct work_struct *work)
>>          * ordered to sync our time by the host.
>>          */
>>         if (abs(delta) > MAXPHASE || wrk->flags & ICTIMESYNCFLAG_SYNC) {
>> +               local_irq_restore(flags);
>>                 do_settimeofday64(&host_ts);
>>                 return;
>>         }
>> @@ -232,6 +236,8 @@ static void hv_set_host_time(struct work_struct *work)
>>         ret = do_adjtimex(&txc);
>>         if (ret)
>>                 pr_debug("Failed to adjust system time: %d\n", ret);
>> +
>> +       local_irq_restore(flags);
>
> This seems like a long time to disable irqs for what your trying to
> do. I'd guess you really only want to disable irqs while you aquire
> the host and guest timestamps (so they are as close together as
> possible).  Since the delta is then calculated, I'm not sure what
> disabling irqs for calling adjtimex gets you.
>

True,

interrupts disabling would only be beneficial for the
do_settimeofday64() case but we can't actually do it there. I'll shorten
the interrupts disabling to the delta calculation only.

-- 
  Vitaly

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[PATCH v2 0/4] hv_util: adjust system time smoothly Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-01-04 18:40 +0100
  [PATCH v2 4/4] hv_util: improve time adjustment accuracy by disabling interrupts Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-01-04 18:50 +0100
    Re: [PATCH v2 4/4] hv_util: improve time adjustment accuracy by  disabling interrupts Stephen Hemminger <stephen@networkplumber.org> - 2017-01-04 20:20 +0100
      Re: [PATCH v2 4/4] hv_util: improve time adjustment accuracy by disabling interrupts Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-01-05 13:40 +0100
        Re: [PATCH v2 4/4] hv_util: improve time adjustment accuracy by  disabling interrupts Stephen Hemminger <stephen@networkplumber.org> - 2017-01-05 18:50 +0100
    Re: [PATCH v2 4/4] hv_util: improve time adjustment accuracy by  disabling interrupts John Stultz <john.stultz@linaro.org> - 2017-01-07 02:10 +0100
      Re: [PATCH v2 4/4] hv_util: improve time adjustment accuracy by disabling interrupts Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-01-09 14:10 +0100
  Re: [PATCH v2 0/4] hv_util: adjust system time smoothly Thomas Gleixner <tglx@linutronix.de> - 2017-01-09 22:30 +0100
    Re: [PATCH v2 0/4] hv_util: adjust system time smoothly Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-01-10 15:40 +0100
      Re: [PATCH v2 0/4] hv_util: adjust system time smoothly Thomas Gleixner <tglx@linutronix.de> - 2017-01-10 16:00 +0100
        [PATCH RFC] hv_utils: implement Hyper-V PTP source Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-01-13 14:10 +0100
          Re: [PATCH RFC] hv_utils: implement Hyper-V PTP source Richard Cochran <richardcochran@gmail.com> - 2017-01-13 16:00 +0100
            Re: [PATCH RFC] hv_utils: implement Hyper-V PTP source Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-01-13 16:40 +0100
          Re: [PATCH RFC] hv_utils: implement Hyper-V PTP source Olaf Hering <olaf@aepfle.de> - 2017-01-13 16:30 +0100
            Re: [PATCH RFC] hv_utils: implement Hyper-V PTP source Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-01-13 16:40 +0100

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