linux-kernel - Re: [PATCH] time, ntp: Do not update time

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Message-ID: <54E7417B.1090900@redhat.com>
Date:	Fri, 20 Feb 2015 09:15:23 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	Jiri Bohac <jbohac@...e.cz>
CC:	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Miroslav Lichvar <mlichvar@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] time, ntp: Do not update time_state in middle of leap
 second [v3]



On 02/19/2015 12:00 PM, Jiri Bohac wrote:
> Hi,
> 
> I'm trying to understand what exactly is going on here...
> 
> On Thu, Feb 12, 2015 at 08:58:19AM -0500, Prarit Bhargava wrote:
>> The test did the following in userspace:
>>
>>         tx.modes = ADJ_STATUS;
>>         tx.status = STA_INS;
>>
>> 	/* send leap second request */
>>         ret = adjtimex(&tx);
>>
>>         /* Check adjtimex output every half second */
>>         now = tx.time.tv_sec;
>>         while (now < next_leap+2) {
>>                 char buf[26];
>>                 ret = adjtimex(&tx);
>>
>>                 ctime_r(&tx.time.tv_sec, buf);
>>                 buf[strlen(buf)-1] = 0; /*remove trailing\n */
>>
>>                 printf("%s + %6ld us\t%s\n",
>>                                 buf,
>>                                 tx.time.tv_usec,
>>                                 time_state_str(ret));
>>                 now = tx.time.tv_sec;
>>                 /* Sleep for another half second */
>>                 ts.tv_sec = 0;
>>                 ts.tv_nsec = NSEC_PER_SEC/2;
>>                 clock_nanosleep(CLOCK_MONOTONIC, 0, &ts, NULL);
>>         }
>>
>> After some investigation it was noted that the test contained a small error:
>> the test does not reinitialize tx.status and reissues the STA_INS every
>> 1/2 second.
> 
> Prarit, can you explain who sets the STA_PLL flag, so that
> process_adj_status() detects a STA_PLL->!STA_PLL transition and
> goes to the branch that sets time_state = TIME_OK?

Jiri,

The test being run is:

https://github.com/johnstultz-work/timetests/blob/master/leap-a-day.c

prior to commit

https://github.com/johnstultz-work/timetests/commit/be4526e8b5d48cd108a8d2cf7f5c8fd763acf421

> 
> Is that ntpd running in parallel with your test program?  If that

No -- ntpd is disabled (chronyd in the case of systemd + current Fedora).

P.
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