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From: Anchal Agarwal <anchalag@amazon.com>
To: <tglx@linutronix.de>, <mingo@redhat.com>, <bp@alien8.de>,
	<hpa@zytor.com>, <x86@kernel.org>, <boris.ostrovsky@oracle.com>,
	<jgross@suse.com>, <linux-pm@vger.kernel.org>,
	<linux-mm@kvack.org>, <kamatam@amazon.com>,
	<sstabellini@kernel.org>, <konrad.wilk@oracle.com>,
	<roger.pau@citrix.com>, <axboe@kernel.dk>, <davem@davemloft.net>,
	<rjw@rjwysocki.net>, <len.brown@intel.com>, <pavel@ucw.cz>,
	<peterz@infradead.org>, <eduval@amazon.com>, <sblbir@amazon.com>,
	<anchalag@amazon.com>, <xen-devel@lists.xenproject.org>,
	<vkuznets@redhat.com>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <dwmw@amazon.co.uk>,
	<fllinden@amaozn.com>, <benh@kernel.crashing.org>
Subject: [RFC PATCH v3 08/12] xen/time: introduce xen_{save,restore}_steal_clock
Date: Fri, 14 Feb 2020 23:26:24 +0000
Message-ID: <489caa869095f77ed8db188d36e858533d7b4d7c.1581721799.git.anchalag@amazon.com> (raw)
In-Reply-To: <cover.1581721799.git.anchalag@amazon.com>

From: Munehisa Kamata <kamatam@amazon.com>

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.

This patch introduces xen_save_steal_clock() which saves current values
in runstate info into per-cpu variables. Its couterpart,
xen_restore_steal_clock(), sets offset if it found the current values in
runstate info are smaller than previous ones. xen_steal_clock() is also
modified to use the offset to ensure that scheduler only sees
monotonically increasing number.

Signed-off-by: Munehisa Kamata <kamatam@amazon.com>
Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
---
 drivers/xen/time.c    | 29 ++++++++++++++++++++++++++++-
 include/xen/xen-ops.h |  2 ++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/time.c b/drivers/xen/time.c
index 0968859c29d0..3560222cc0dd 100644
--- a/drivers/xen/time.c
+++ b/drivers/xen/time.c
@@ -23,6 +23,9 @@ static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
 
 static DEFINE_PER_CPU(u64[4], old_runstate_time);
 
+static DEFINE_PER_CPU(u64, xen_prev_steal_clock);
+static DEFINE_PER_CPU(u64, xen_steal_clock_offset);
+
 /* return an consistent snapshot of 64-bit time/counter value */
 static u64 get64(const u64 *p)
 {
@@ -149,7 +152,7 @@ bool xen_vcpu_stolen(int vcpu)
 	return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
 }
 
-u64 xen_steal_clock(int cpu)
+static u64 __xen_steal_clock(int cpu)
 {
 	struct vcpu_runstate_info state;
 
@@ -157,6 +160,30 @@ u64 xen_steal_clock(int cpu)
 	return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
 }
 
+u64 xen_steal_clock(int cpu)
+{
+	return __xen_steal_clock(cpu) + per_cpu(xen_steal_clock_offset, cpu);
+}
+
+void xen_save_steal_clock(int cpu)
+{
+	per_cpu(xen_prev_steal_clock, cpu) = xen_steal_clock(cpu);
+}
+
+void xen_restore_steal_clock(int cpu)
+{
+	u64 steal_clock = __xen_steal_clock(cpu);
+
+	if (per_cpu(xen_prev_steal_clock, cpu) > steal_clock) {
+		/* Need to update the offset */
+		per_cpu(xen_steal_clock_offset, cpu) =
+		    per_cpu(xen_prev_steal_clock, cpu) - steal_clock;
+	} else {
+		/* Avoid unnecessary steal clock warp */
+		per_cpu(xen_steal_clock_offset, cpu) = 0;
+	}
+}
+
 void xen_setup_runstate_info(int cpu)
 {
 	struct vcpu_register_runstate_memory_area area;
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 3b3992b5b0c2..12b3f4474a05 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -37,6 +37,8 @@ void xen_time_setup_guest(void);
 void xen_manage_runstate_time(int action);
 void xen_get_runstate_snapshot(struct vcpu_runstate_info *res);
 u64 xen_steal_clock(int cpu);
+void xen_save_steal_clock(int cpu);
+void xen_restore_steal_clock(int cpu);
 
 int xen_setup_shutdown_event(void);
 
-- 
2.24.1.AMZN


  parent reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14 23:21 [RFC RESEND PATCH v3 00/12] Enable PM hibernation on guest VMs Anchal Agarwal
2020-02-14 23:22 ` [RFC PATCH v3 01/12] xen/manage: keep track of the on-going suspend mode Anchal Agarwal
2020-02-14 23:23 ` [RFC PATCH v3 02/12] xenbus: add freeze/thaw/restore callbacks support Anchal Agarwal
2020-02-14 23:23 ` [RFC PATCH v3 03/12] x86/xen: Introduce new function to map HYPERVISOR_shared_info on Resume Anchal Agarwal
2020-02-14 23:24 ` [RFC PATCH v3 04/12] x86/xen: add system core suspend and resume callbacks Anchal Agarwal
2020-02-14 23:24 ` [RFC PATCH v3 05/12] xen-netfront: add callbacks for PM suspend and hibernation support Anchal Agarwal
2020-02-14 23:25 ` [RFC PATCH v3 06/12] xen-blkfront: add callbacks for PM suspend and hibernation Anchal Agarwal
2020-02-17 10:05   ` Roger Pau Monné
2020-02-17 23:05     ` Anchal Agarwal
2020-02-18  9:16       ` Roger Pau Monné
2020-02-19 18:04         ` Anchal Agarwal
2020-02-20  8:39           ` Roger Pau Monné
2020-02-20  8:54             ` [Xen-devel] " Durrant, Paul
2020-02-20 15:45               ` Roger Pau Monné
2020-02-20 16:23                 ` Durrant, Paul
2020-02-20 16:48                   ` Roger Pau Monné
2020-02-20 17:01                     ` Durrant, Paul
2020-02-14 23:25 ` [RFC PATCH v3 07/12] genirq: Shutdown irq chips in suspend/resume during hibernation Anchal Agarwal
2020-02-14 23:26 ` Anchal Agarwal [this message]
2020-02-14 23:27 ` [RFC PATCH v3 09/12] x86/xen: save and restore steal clock Anchal Agarwal
2020-02-14 23:27 ` [RFC PATCH v3 10/12] xen: Introduce wrapper for save/restore sched clock offset Anchal Agarwal
2020-02-14 23:27 ` [RFC PATCH v3 11/12] xen: Update sched clock offset to avoid system instability in hibernation Anchal Agarwal
2020-02-14 23:28 ` [RFC PATCH v3 12/12] PM / hibernate: update the resume offset on SNAPSHOT_SET_SWAP_AREA Anchal Agarwal
  -- strict thread matches above, loose matches on Subject: below --
2020-02-12 22:33 [RFC PATCH v3 08/12] xen/time: introduce xen_{save,restore}_steal_clock Anchal Agarwal

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