linux-kernel - [PATCH v3 08/11] x86/xen: save and restore steal clock during PM hibernation

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Message-ID: <5c3be5c7519b1f63a51b08abc388c33bd6f66661.1598042152.git.anchalag@amazon.com>
Date:   Fri, 21 Aug 2020 22:29:55 +0000
From:   Anchal Agarwal <anchalag@...zon.com>
To:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <hpa@...or.com>, <x86@...nel.org>, <boris.ostrovsky@...cle.com>,
        <jgross@...e.com>, <linux-pm@...r.kernel.org>,
        <linux-mm@...ck.org>, <kamatam@...zon.com>,
        <sstabellini@...nel.org>, <konrad.wilk@...cle.com>,
        <roger.pau@...rix.com>, <axboe@...nel.dk>, <davem@...emloft.net>,
        <rjw@...ysocki.net>, <len.brown@...el.com>, <pavel@....cz>,
        <peterz@...radead.org>, <eduval@...zon.com>, <sblbir@...zon.com>,
        <anchalag@...zon.com>, <xen-devel@...ts.xenproject.org>,
        <vkuznets@...hat.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dwmw@...zon.co.uk>,
        <benh@...nel.crashing.org>
Subject: [PATCH v3 08/11] x86/xen: save and restore steal clock during PM
 hibernation

Save/restore steal times in syscore suspend/resume during PM
hibernation. Commit '5e25f5db6abb9: ("xen/time: do not
decrease steal time after live migration on xen")' fixes xen
guest steal time handling during migration. A similar issue is seen
during PM hibernation.
Currently, steal time accounting code in scheduler expects steal clock
callback to provide monotonically increasing value. If the accounting
code receives a smaller value than previous one, it uses a negative
value to calculate steal time and results in incorrectly updated idle
and steal time accounting. This breaks userspace tools which read
/proc/stat.

top - 08:05:35 up  2:12,  3 users,  load average: 0.00, 0.07, 0.23
Tasks:  80 total,   1 running,  79 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.0%us,  0.0%sy,  0.0%ni,30100.0%id,  0.0%wa,  0.0%hi, 0.0%si,-1253874204672.0%st

This can actually happen when a Xen PVHVM guest gets restored from
hibernation, because such a restored guest is just a fresh domain from
Xen perspective and the time information in runstate info starts over
from scratch.

Changelog:
v1->v2: Removed patches that introduced new function calls for saving/restoring
        sched clock offset and using existing ones that are used during LM

Signed-off-by: Anchal Agarwal <anchalag@...zon.com>
---
 arch/x86/xen/suspend.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
index 550aa0fc9465..b12db6966af6 100644
--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c
@@ -99,6 +99,7 @@ static int xen_syscore_suspend(void)
 
 	gnttab_suspend();
 
+	xen_manage_runstate_time(-1);
 	xrfp.domid = DOMID_SELF;
 	xrfp.gpfn = __pa(HYPERVISOR_shared_info) >> PAGE_SHIFT;
 
@@ -119,7 +120,7 @@ static void xen_syscore_resume(void)
 	xen_hvm_map_shared_info();
 
 	pvclock_resume();
-
+	xen_manage_runstate_time(0);
 	gnttab_resume();
 }
 
-- 
2.16.6