From: Pavel Tatashin <pasha.tatashin@oracle.com>
To: tglx@linutronix.de
Cc: Steven Sistare <steven.sistare@oracle.com>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
linux@armlinux.org.uk, schwidefsky@de.ibm.com,
Heiko Carstens <heiko.carstens@de.ibm.com>,
John Stultz <john.stultz@linaro.org>,
sboyd@codeaurora.org, x86@kernel.org,
LKML <linux-kernel@vger.kernel.org>,
mingo@redhat.com, hpa@zytor.com, douly.fnst@cn.fujitsu.com,
peterz@infradead.org, prarit@redhat.com, feng.tang@intel.com,
Petr Mladek <pmladek@suse.com>,
gnomes@lxorguk.ukuu.org.uk, linux-s390@vger.kernel.org
Subject: Re: [PATCH v12 09/11] x86/tsc: prepare for early sched_clock
Date: Sat, 23 Jun 2018 17:29:35 -0400 [thread overview]
Message-ID: <CAGM2reYQx769omkWVweEcTMy8WNrKOiuUVo4OFWNh4zW-rc4pg@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1806232210110.8650@nanos.tec.linutronix.de>
> So you forgot to answer this question. I did not find a system yet, which
> actually exposes this behaviour on mainline.
>
> Is this an artifact of your early sched clock thing?
>
Yes, it is. Let me explain how it happens.
So, the problem is introduced in patch "sched: early boot clock" by this change:
- if (unlikely(!sched_clock_running))
- return 0ull;
+ /* Use early clock until sched_clock_init_late() */
+ if (unlikely(sched_clock_running < 2))
+ return sched_clock() + __sched_clock_offset;
As soon as sched_clock() starts output non-zero values, we start
output time without correcting the output as it is done in
sched_clock_local() where unstable TSC and backward motion are
detected. But, since early in boot interrupts are disabled, we cannot
really correct invalid time, and therefore must rely on sched_clock()
to provide us with a contiguous and sane time. In earlier versions of
this project, I was solving this problem by adjusting
__sched_clock_offset every time sched_clock()'s continuity was changed
by using a callback function into sched/clock.c. But, Peter was
against that approach.
next prev parent reply other threads:[~2018-06-23 21:30 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-21 21:25 [PATCH v12 00/11] Early boot time stamps for x86 Pavel Tatashin
2018-06-21 21:25 ` [PATCH v12 01/11] x86: text_poke() may access uninitialized struct pages Pavel Tatashin
2018-06-21 21:37 ` Randy Dunlap
2018-06-25 8:14 ` Peter Zijlstra
2018-06-25 8:39 ` Thomas Gleixner
2018-06-25 9:09 ` Peter Zijlstra
2018-06-25 9:18 ` Thomas Gleixner
2018-06-25 9:22 ` Peter Zijlstra
2018-06-25 12:32 ` Pavel Tatashin
2018-06-25 13:48 ` Peter Zijlstra
2018-06-25 14:06 ` Pavel Tatashin
2018-06-21 21:25 ` [PATCH v12 02/11] x86: initialize static branching early Pavel Tatashin
2018-06-23 9:16 ` Borislav Petkov
2018-06-23 13:11 ` Pavel Tatashin
2018-06-21 21:25 ` [PATCH v12 03/11] x86/tsc: redefine notsc to behave as tsc=unstable Pavel Tatashin
2018-06-23 13:32 ` Thomas Gleixner
2018-06-21 21:25 ` [PATCH v12 04/11] kvm/x86: remove kvm memblock dependency Pavel Tatashin
2018-06-23 13:36 ` Thomas Gleixner
2018-07-05 16:12 ` Paolo Bonzini
2018-07-06 9:24 ` Thomas Gleixner
2018-07-06 9:36 ` Paolo Bonzini
2018-07-06 9:45 ` Thomas Gleixner
2018-07-06 10:08 ` Paolo Bonzini
2018-07-06 10:44 ` Thomas Gleixner
2018-07-06 10:50 ` Thomas Gleixner
2018-07-06 15:03 ` Pavel Tatashin
2018-07-06 15:09 ` Paolo Bonzini
2018-06-21 21:25 ` [PATCH v12 05/11] s390/time: add read_persistent_wall_and_boot_offset() Pavel Tatashin
2018-06-25 7:07 ` Martin Schwidefsky
2018-06-25 12:45 ` Pavel Tatashin
2018-06-21 21:25 ` [PATCH v12 06/11] time: replace read_boot_clock64() with read_persistent_wall_and_boot_offset() Pavel Tatashin
2018-06-23 13:49 ` Thomas Gleixner
2018-06-21 21:25 ` [PATCH v12 07/11] s390/time: remove read_boot_clock64() Pavel Tatashin
2018-06-21 21:25 ` [PATCH v12 08/11] ARM/time: " Pavel Tatashin
2018-06-23 13:52 ` Thomas Gleixner
2018-06-21 21:25 ` [PATCH v12 09/11] x86/tsc: prepare for early sched_clock Pavel Tatashin
2018-06-23 16:50 ` Thomas Gleixner
2018-06-23 18:49 ` Pavel Tatashin
2018-06-23 20:11 ` Thomas Gleixner
2018-06-23 21:29 ` Pavel Tatashin [this message]
2018-06-23 23:38 ` Thomas Gleixner
2018-06-24 2:43 ` Pavel Tatashin
2018-06-24 7:30 ` Thomas Gleixner
2018-06-26 15:42 ` Thomas Gleixner
2018-06-26 18:42 ` Pavel Tatashin
2018-06-26 19:47 ` Pavel Tatashin
2018-06-28 7:31 ` Thomas Gleixner
2018-06-28 10:43 ` Thomas Gleixner
2018-06-28 11:46 ` Peter Zijlstra
2018-06-28 12:27 ` Thomas Gleixner
2018-06-28 19:42 ` Pavel Tatashin
2018-06-29 7:30 ` Thomas Gleixner
2018-06-29 8:57 ` Pavel Tatashin
2018-07-03 20:59 ` Thomas Gleixner
2018-07-02 17:18 ` Konrad Rzeszutek Wilk
2018-06-29 14:30 ` Andy Shevchenko
2018-06-29 17:50 ` Andy Shevchenko
2018-07-09 23:16 ` Boris Ostrovsky
2018-06-21 21:25 ` [PATCH v12 10/11] sched: early boot clock Pavel Tatashin
2018-06-25 8:55 ` Peter Zijlstra
2018-06-25 12:44 ` Pavel Tatashin
2018-06-25 19:23 ` Pavel Tatashin
2018-06-26 9:00 ` Peter Zijlstra
2018-06-26 11:27 ` Pavel Tatashin
2018-06-26 11:51 ` Pavel Tatashin
2018-06-26 15:07 ` Peter Zijlstra
2018-06-21 21:25 ` [PATCH v12 11/11] x86/tsc: use tsc early Pavel Tatashin
2018-06-23 16:56 ` Thomas Gleixner
2018-06-23 21:38 ` Pavel Tatashin
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=CAGM2reYQx769omkWVweEcTMy8WNrKOiuUVo4OFWNh4zW-rc4pg@mail.gmail.com \
--to=pasha.tatashin@oracle.com \
--cc=daniel.m.jordan@oracle.com \
--cc=douly.fnst@cn.fujitsu.com \
--cc=feng.tang@intel.com \
--cc=gnomes@lxorguk.ukuu.org.uk \
--cc=heiko.carstens@de.ibm.com \
--cc=hpa@zytor.com \
--cc=john.stultz@linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=pmladek@suse.com \
--cc=prarit@redhat.com \
--cc=sboyd@codeaurora.org \
--cc=schwidefsky@de.ibm.com \
--cc=steven.sistare@oracle.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/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).