From: Peter Zijlstra <peterz@infradead.org>
To: John Stultz <john.stultz@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Prarit Bhargava <prarit@redhat.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Richard Cochran <richardcochran@gmail.com>,
Jan Kara <jack@suse.cz>, Jiri Bohac <jbohac@suse.cz>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Shuah Khan <shuahkh@osg.samsung.com>
Subject: Re: [RFC][PATCH 4/4] time: Do leapsecond adjustment in gettime fastpaths
Date: Fri, 5 Jun 2015 09:29:13 +0200 [thread overview]
Message-ID: <20150605072913.GD19282@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CALAqxLUo75Y-2Rt4fEdwq=V1AOU5uGsE2VH=0cP_FiSUXW+OyQ@mail.gmail.com>
On Thu, Jun 04, 2015 at 05:08:11PM -0700, John Stultz wrote:
> I'm not sure how this follows. Leap smearing is a different behavior
> and I'd like to support it (as a separate clockid) as well, but adding
> that support doesn't change that the existing behavior applying the
> leapsecond to UTC/CLOCK_REALTIME via a timer results in behavior that
> isn't strictly correct.
So the big problem of course is that your patches do not handle the VDSO
time read, and that is the biggest source of userspace time.
So userspace will still see incorrect time, only in-kernel users (timers
being your prime example) get the leap second at the 'right' place.
Also note that your argument that timers will now get the correct time
is subject to the very same timer interrupt jitter as driving the leap
second stuff from an hrtimer itself -- they're all timers.
That leaves the question; for who is this exact second edge important?
next prev parent reply other threads:[~2015-06-05 7:29 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-29 20:24 [RFC][PATCH 0/4] Fixes for leapsecond expiring early ABS_TIME CLOCK_REALTIME timers John Stultz
2015-05-29 20:24 ` [RFC][PATCH 1/4] selftests: timers: Add leap-second timer edge testing to leap-a-day.c John Stultz
2015-05-29 20:24 ` [RFC][PATCH 2/4] timer_list: Add the base offset so remaining nsecs are accurate for non monotonic timers John Stultz
2015-05-29 20:24 ` [RFC][PATCH 3/4] ntp: Use printk_deferred in leapsecond path John Stultz
2015-06-02 10:31 ` Jiri Bohac
2015-06-02 10:43 ` Jiri Kosina
2015-06-02 16:14 ` John Stultz
2015-06-02 16:04 ` John Stultz
2015-05-29 20:24 ` [RFC][PATCH 4/4] time: Do leapsecond adjustment in gettime fastpaths John Stultz
2015-05-31 16:05 ` Richard Cochran
2015-06-02 9:01 ` Ingo Molnar
2015-06-02 9:21 ` Peter Zijlstra
2015-06-02 14:09 ` John Stultz
2015-06-02 15:52 ` John Stultz
2015-06-03 9:04 ` Ingo Molnar
2015-06-03 17:44 ` John Stultz
2015-06-04 6:48 ` Ingo Molnar
2015-06-05 0:08 ` John Stultz
2015-06-05 7:29 ` Peter Zijlstra [this message]
2015-06-05 9:04 ` Richard Cochran
2015-06-05 9:10 ` Peter Zijlstra
2015-06-05 14:12 ` Richard Cochran
2015-06-05 17:28 ` John Stultz
2015-06-06 9:44 ` Thomas Gleixner
2015-06-08 17:55 ` John Stultz
2015-06-08 19:05 ` Thomas Gleixner
2015-06-08 20:02 ` Thomas Gleixner
2015-06-05 11:37 ` Prarit Bhargava
2015-06-05 12:07 ` Thomas Gleixner
2015-06-05 14:22 ` Richard Cochran
2015-06-05 17:24 ` John Stultz
2015-05-31 13:55 ` [RFC][PATCH 0/4] Fixes for leapsecond expiring early ABS_TIME CLOCK_REALTIME timers Prarit Bhargava
2015-06-01 11:57 ` Prarit Bhargava
2015-06-01 17:02 ` John Stultz
2015-06-01 17:43 ` Prarit Bhargava
2015-06-01 20:18 ` Daniel Bristot de Oliveira
2015-06-01 20:32 ` John Stultz
2015-06-01 21:42 ` Prarit Bhargava
2015-06-01 22:29 ` Daniel Bristot de Oliveira
2015-06-02 6:19 ` John Stultz
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