From: Ingo Molnar <mingo@kernel.org>
To: John Stultz <john.stultz@linaro.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
Xunlei Pang <pang.xunlei@linaro.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 17/21] time: Fix a bug in timekeeping_suspend() with no persistent clock
Date: Fri, 3 Apr 2015 08:16:08 +0200 [thread overview]
Message-ID: <20150403061608.GA12625@gmail.com> (raw)
In-Reply-To: <1427945681-29972-18-git-send-email-john.stultz@linaro.org>
* John Stultz <john.stultz@linaro.org> wrote:
> From: Xunlei Pang <pang.xunlei@linaro.org>
>
> When there's no persistent clock, normally timekeeping_suspend_time
> should always be zero, but this can break in timekeeping_suspend().
>
> At T1, there was a system suspend, so old_delta was assigned T1.
> After some time, one time adjustment happened, and xtime got the
> value of T1-dt(0s<dt<2s). Then, there comes another system suspend
> soon after this adjustment, obviously we will get a small negative
> delta_delta, resulting in a negative timekeeping_suspend_time.
>
> This is problematic, when doing timekeeping_resume() if there is
> no nonstop clocksource for example, it will hit the else leg and
> inject the improper sleeptime which is the wrong logic.
>
> So, we can solve this problem by only doing delta related code when
> the persistent clock is existent. Actually the code only makes sense
> for persistent clock cases.
What's the effect in practice of such negative delta_delta values?
What kind of effects would users see from this?
Thanks,
Ingo
next prev parent reply other threads:[~2015-04-03 6:16 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-02 3:34 [PATCH 00/21] 4.1 time and rtc changes for tip/timers/core John Stultz
2015-04-02 3:34 ` [PATCH 01/21] time: Add y2038 safe read_boot_clock64() John Stultz
2015-04-03 8:15 ` [tip:timers/core] " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 02/21] time: Add y2038 safe read_persistent_clock64() John Stultz
2015-04-03 8:15 ` [tip:timers/core] " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 03/21] time: Add y2038 safe update_persistent_clock64() John Stultz
2015-04-03 8:16 ` [tip:timers/core] time: Add y2038 safe update_persistent_clock64( ) tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 04/21] ARM: OMAP: 32k counter: Provide y2038-safe omap_read_persistent_clock() replacement John Stultz
2015-04-03 8:16 ` [tip:timers/core] " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 05/21] ARM: tegra: clock: Provide y2038-safe tegra_read_persistent_clock() replacement John Stultz
2015-04-03 8:16 ` [tip:timers/core] clocksource/drivers/tegra: " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 06/21] ARM: time: Provide read_boot_clock64() and read_persistent_clock64() John Stultz
2015-04-03 8:17 ` [tip:timers/core] ARM, clocksource/drivers: Provide read_boot_clock64() and read_persistent_clock64() and use them tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 07/21] rtc: Provide y2038 safe rtc_class_ops.set_mmss() replacement John Stultz
2015-04-03 8:17 ` [tip:timers/core] drivers/rtc: " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 08/21] rtc/test: Update driver to address y2038/y2106 issues John Stultz
2015-04-03 8:17 ` [tip:timers/core] drivers/rtc/test: " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 09/21] rtc/ab3100: " John Stultz
2015-04-03 8:17 ` [tip:timers/core] drivers/rtc/ab3100: " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 10/21] rtc/mc13xxx: " John Stultz
2015-04-03 8:18 ` [tip:timers/core] drivers/rtc/mc13xxx: " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 11/21] rtc/mxc: Modify rtc_update_alarm() not to touch the alarm time John Stultz
2015-04-03 8:18 ` [tip:timers/core] drivers/rtc/mxc: " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 12/21] rtc/mxc: Convert get_alarm_or_time()/set_alarm_or_time() to use time64_t John Stultz
2015-04-03 8:18 ` [tip:timers/core] drivers/rtc/mxc: Convert get_alarm_or_time()/ set_alarm_or_time() " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 13/21] rtc/mxc: Update driver to address y2038/y2106 issues John Stultz
2015-04-03 8:19 ` [tip:timers/core] drivers/rtc/mxc: Update driver to address y2038 /y2106 issues tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 14/21] alpha: rtc: Change to use rtc_class_ops's set_mmss64() John Stultz
2015-04-03 8:19 ` [tip:timers/core] alpha, rtc: Change to use rtc_class_ops' s set_mmss64() tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 15/21] time: Don't build timekeeping_inject_sleeptime64() if no one uses it John Stultz
2015-04-03 8:19 ` [tip:timers/core] time: Don' t " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 16/21] rtc: Remove redundant rtc_valid_tm() from rtc_resume() John Stultz
2015-04-03 8:19 ` [tip:timers/core] drivers/rtc: " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 17/21] time: Fix a bug in timekeeping_suspend() with no persistent clock John Stultz
2015-04-03 6:16 ` Ingo Molnar [this message]
2015-04-03 8:20 ` [tip:timers/core] " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 18/21] time: rtc: Don't bother into rtc_resume() for the nonstop clocksource John Stultz
2015-04-03 8:20 ` [tip:timers/core] time, drivers/rtc: Don't bother with rtc_resume () " tip-bot for Xunlei Pang
2015-04-02 3:34 ` [PATCH 19/21] clocksource: Improve comment explaining clocks_calc_max_nsecs()'s 50% safety margin John Stultz
2015-04-02 8:50 ` Peter Zijlstra
2015-04-02 17:30 ` John Stultz
2015-04-02 18:34 ` Peter Zijlstra
2015-04-02 18:41 ` John Stultz
2015-04-02 18:43 ` Peter Zijlstra
2015-04-02 18:50 ` John Stultz
2015-04-02 19:04 ` Peter Zijlstra
2015-04-03 8:20 ` [tip:timers/core] " tip-bot for John Stultz
2015-04-02 3:34 ` [PATCH 20/21] timekeeping: Change timekeeping_check_update() to take a tk_read_base John Stultz
2015-04-02 3:34 ` [PATCH 21/21] time: Rework debugging variables so they aren't global John Stultz
2015-04-02 7:47 ` Peter Zijlstra
2015-04-02 7:51 ` Ingo Molnar
2015-04-02 8:36 ` Peter Zijlstra
2015-04-02 8:41 ` Peter Zijlstra
2015-04-02 17:32 ` John Stultz
2015-04-03 6:21 ` Ingo Molnar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150403061608.GA12625@gmail.com \
--to=mingo@kernel.org \
--cc=john.stultz@linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pang.xunlei@linaro.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).