From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: John Stultz <john.stultz@linaro.org>
Cc: "devel\@linuxdriverproject.org" <devel@linuxdriverproject.org>,
lkml <linux-kernel@vger.kernel.org>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Thomas Gleixner <tglx@linutronix.de>,
Alex Ng <alexng@microsoft.com>,
Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH v2 4/4] hv_util: improve time adjustment accuracy by disabling interrupts
Date: Mon, 09 Jan 2017 14:05:43 +0100 [thread overview]
Message-ID: <8737gs8jtk.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <CALAqxLWiHDBnHxJGdmmb=L-bSLqqc=_xOa6KuPBYo08WZQP6HQ@mail.gmail.com> (John Stultz's message of "Fri, 6 Jan 2017 17:02:54 -0800")
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
next prev parent reply other threads:[~2017-01-09 13:05 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-04 17:24 [PATCH v2 0/4] hv_util: adjust system time smoothly Vitaly Kuznetsov
2017-01-04 17:24 ` [PATCH v2 1/4] timekeeping: export do_adjtimex() to modules Vitaly Kuznetsov
2017-01-07 1:06 ` John Stultz
2017-01-09 13:03 ` Vitaly Kuznetsov
2017-01-04 17:24 ` [PATCH v2 2/4] hv_util: switch to using timespec64 Vitaly Kuznetsov
2017-01-07 1:04 ` John Stultz
2017-01-04 17:24 ` [PATCH v2 3/4] hv_util: use do_adjtimex() to update system time Vitaly Kuznetsov
2017-01-04 19:09 ` Stephen Hemminger
2017-01-05 12:37 ` Vitaly Kuznetsov
2017-01-07 0:56 ` John Stultz
2017-01-04 17:24 ` [PATCH v2 4/4] hv_util: improve time adjustment accuracy by disabling interrupts Vitaly Kuznetsov
2017-01-04 19:17 ` Stephen Hemminger
2017-01-05 12:35 ` Vitaly Kuznetsov
2017-01-05 17:39 ` Stephen Hemminger
2017-01-07 1:02 ` John Stultz
2017-01-09 13:05 ` Vitaly Kuznetsov [this message]
2017-01-09 21:27 ` [PATCH v2 0/4] hv_util: adjust system time smoothly Thomas Gleixner
2017-01-10 14:30 ` Vitaly Kuznetsov
2017-01-10 14:58 ` Thomas Gleixner
2017-01-13 13:05 ` [PATCH RFC] hv_utils: implement Hyper-V PTP source Vitaly Kuznetsov
2017-01-13 14:50 ` Richard Cochran
2017-01-13 15:38 ` Vitaly Kuznetsov
2017-01-13 15:21 ` Olaf Hering
2017-01-13 15:37 ` Vitaly Kuznetsov
2017-01-16 19:29 ` Thomas Gleixner
2017-01-17 9:53 ` Vitaly Kuznetsov
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