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Subject: Re: [PATCH v2] xen: Fix x86 sched_clock() interface for xen
To:     Juergen Gross <jgross@suse.com>, linux-kernel@vger.kernel.org,
        xen-devel@lists.xenproject.org, x86@kernel.org
Cc:     boris.ostrovsky@oracle.com, sstabellini@kernel.org, hpa@zytor.com,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        stable@vger.kernel.org
References: <20190111120805.24852-1-jgross@suse.com>
From:   Hans van Kranenburg <hans@knorrie.org>
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Message-ID: <74aafdff-c7d5-b9aa-c3fb-3787d36c7bbe@knorrie.org>
Date:   Fri, 11 Jan 2019 14:12:59 +0100
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,

On 1/11/19 1:08 PM, Juergen Gross wrote:
> Commit f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable'
> sched_clock() interface") broke Xen guest time handling across
> migration:
> 
> [  187.249951] Freezing user space processes ... (elapsed 0.001 seconds) done.
> [  187.251137] OOM killer disabled.
> [  187.251137] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
> [  187.252299] suspending xenstore...
> [  187.266987] xen:grant_table: Grant tables using version 1 layout
> [18446743811.706476] OOM killer enabled.
> [18446743811.706478] Restarting tasks ... done.
> [18446743811.720505] Setting capacity to 16777216
> 
> Fix that by setting xen_sched_clock_offset at resume time to ensure a
> monotonic clock value.
> 
> [...]

I'm throwing around a PV domU over a bunch of test servers with live
migrate now, and in between the kernel logging, I'm seeing this:

[Fri Jan 11 13:58:42 2019] Freezing user space processes ... (elapsed
0.002 seconds) done.
[Fri Jan 11 13:58:42 2019] OOM killer disabled.
[Fri Jan 11 13:58:42 2019] Freezing remaining freezable tasks ...
(elapsed 0.000 seconds) done.
[Fri Jan 11 13:58:42 2019] suspending xenstore...
[Fri Jan 11 13:58:42 2019] ------------[ cut here ]------------
[Fri Jan 11 13:58:42 2019] Current state: 1
[Fri Jan 11 13:58:42 2019] WARNING: CPU: 3 PID: 0 at
kernel/time/clockevents.c:133 clockevents_switch_state+0x48/0xe0
[Fri Jan 11 13:58:42 2019] Modules linked in:
[Fri Jan 11 13:58:42 2019] CPU: 3 PID: 0 Comm: swapper/3 Not tainted
4.19.14+ #1
[Fri Jan 11 13:58:42 2019] RIP: e030:clockevents_switch_state+0x48/0xe0
[Fri Jan 11 13:58:42 2019] Code: 8b 0c cd 40 ee 00 82 e9 d6 5b d1 00 80
3d 8e 8d 43 01 00 75 17 89 c6 48 c7 c7 92 62 1f 82 c6 05 7c 8d 43 01 01
e8 f8 22 f8 ff <0f> 0b 5b 5d f3 c3 83 e2 01 74 f7 48 8b 47 48 48 85 c0
74 69 48 89
[Fri Jan 11 13:58:42 2019] RSP: e02b:ffffc90000787e30 EFLAGS: 00010082
[Fri Jan 11 13:58:42 2019] RAX: 0000000000000000 RBX: ffff88805df94d80
RCX: 0000000000000006
[Fri Jan 11 13:58:42 2019] RDX: 0000000000000007 RSI: 0000000000000001
RDI: ffff88805df963f0
[Fri Jan 11 13:58:42 2019] RBP: 0000000000000004 R08: 0000000000000000
R09: 0000000000000119
[Fri Jan 11 13:58:42 2019] R10: 0000000000000020 R11: ffffffff82af4e2d
R12: ffff88805df9ca40
[Fri Jan 11 13:58:42 2019] R13: 0000000dd28d6ca6 R14: 0000000000000000
R15: 0000000000000000
[Fri Jan 11 13:58:42 2019] FS:  00007f34193ce040(0000)
GS:ffff88805df80000(0000) knlGS:0000000000000000
[Fri Jan 11 13:58:42 2019] CS:  e033 DS: 002b ES: 002b CR0: 0000000080050033
[Fri Jan 11 13:58:42 2019] CR2: 00007f6220be50e1 CR3: 000000005ce5c000
CR4: 0000000000002660
[Fri Jan 11 13:58:42 2019] Call Trace:
[Fri Jan 11 13:58:42 2019]  tick_program_event+0x4b/0x70
[Fri Jan 11 13:58:42 2019]  hrtimer_try_to_cancel+0xa8/0x100
[Fri Jan 11 13:58:42 2019]  hrtimer_cancel+0x10/0x20
[Fri Jan 11 13:58:42 2019]  __tick_nohz_idle_restart_tick+0x45/0xd0
[Fri Jan 11 13:58:42 2019]  tick_nohz_idle_exit+0x93/0xa0
[Fri Jan 11 13:58:42 2019]  do_idle+0x149/0x260
[Fri Jan 11 13:58:42 2019]  cpu_startup_entry+0x6a/0x70
[Fri Jan 11 13:58:42 2019] ---[ end trace 519c07d1032908f8 ]---
[Fri Jan 11 13:58:42 2019] xen:grant_table: Grant tables using version 1
layout
[Fri Jan 11 13:58:42 2019] OOM killer enabled.
[Fri Jan 11 13:58:42 2019] Restarting tasks ... done.
[Fri Jan 11 13:58:42 2019] Setting capacity to 6291456
[Fri Jan 11 13:58:42 2019] Setting capacity to 10485760

This always happens on every *first* live migrate that I do after
starting the domU.

OTOH, With v1 I've indeed also observed the 'leftover' time jump on the
first line when resuming. It didn't happen always, but it seems to not
happen anymore at all now, so that's good.

Hans