Re: [PATCH] kvmclock: set scheduler clock stable
On 29/04/2015 03:47, Marcelo Tosatti wrote:
On Thu, Apr 23, 2015 at 05:12:42PM -0400, Luiz Capitulino wrote:
If you try to enable NOHZ_FULL on a guest today, you'll get
the following error when the guest tries to deactivate the
scheduler tick:
WARNING: CPU: 3 PID: 2182 at kernel/time/tick-sched.c:192
can_stop_full_tick+0xb9/0x290()
NO_HZ FULL will not work with unstable sched clock
CPU: 3 PID: 2182 Comm: kworker/3:1 Not tainted 4.0.0-10545-gb9bb6fb #204
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Workqueue: events flush_to_ldisc
8162a0c7 88011f583e88 814e6ba0 0002
88011f583ed8 88011f583ec8 8104d095 88011f583eb8
0003 0001 0001
Call Trace:
IRQ [814e6ba0] dump_stack+0x4f/0x7b
[8104d095] warn_slowpath_common+0x85/0xc0
[8104d146] warn_slowpath_fmt+0x46/0x50
[810bd2a9] can_stop_full_tick+0xb9/0x290
[810bd9ed] tick_nohz_irq_exit+0x8d/0xb0
[810511c5] irq_exit+0xc5/0x130
[814f180a] smp_apic_timer_interrupt+0x4a/0x60
[814eff5e] apic_timer_interrupt+0x6e/0x80
EOI [814ee5d1] ? _raw_spin_unlock_irqrestore+0x31/0x60
[8108bbc8] __wake_up+0x48/0x60
[8134836c] n_tty_receive_buf_common+0x49c/0xba0
[8134a6bf] ? tty_ldisc_ref+0x1f/0x70
[81348a84] n_tty_receive_buf2+0x14/0x20
[8134b390] flush_to_ldisc+0xe0/0x120
[81064d05] process_one_work+0x1d5/0x540
[81064c81] ? process_one_work+0x151/0x540
[81065191] worker_thread+0x121/0x470
[81065070] ? process_one_work+0x540/0x540
[8106b4df] kthread+0xef/0x110
[8106b3f0] ? __kthread_parkme+0xa0/0xa0
[814ef4f2] ret_from_fork+0x42/0x70
[8106b3f0] ? __kthread_parkme+0xa0/0xa0
---[ end trace 06e3507544a38866 ]---
However, it turns out that kvmclock does provide a stable
sched_clock callback. So, let the scheduler know this which
in turn makes NOHZ_FULL work in the guest.
Signed-off-by: Marcelo Tosatti mtosa...@redhat.com
Signed-off-by: Luiz Capitulino lcapitul...@redhat.com
---
PS: Original author of this patch is Marcelo. I did most of the
testing and backported it to an older real-time kernel tree. Works
like a charm.
arch/x86/kernel/kvmclock.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 42caaef..4e03921 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -24,6 +24,7 @@
#include linux/percpu.h
#include linux/hardirq.h
#include linux/memblock.h
+#include linux/sched.h
#include asm/x86_init.h
#include asm/reboot.h
@@ -265,6 +266,8 @@ void __init kvmclock_init(void)
if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
+
+set_sched_clock_stable();
}
int __init kvm_setup_vsyscall_timeinfo(void)
--
1.9.3
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Ping?
6 days, half of them during the merge window is not such a terrible
roundtrip. Anyhow I've applied the patch and will probably push to
kvm/queue today.
Paolo
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Re: [PATCH] kvmclock: set scheduler clock stable
On Thu, Apr 23, 2015 at 05:12:42PM -0400, Luiz Capitulino wrote:
If you try to enable NOHZ_FULL on a guest today, you'll get
the following error when the guest tries to deactivate the
scheduler tick:
WARNING: CPU: 3 PID: 2182 at kernel/time/tick-sched.c:192
can_stop_full_tick+0xb9/0x290()
NO_HZ FULL will not work with unstable sched clock
CPU: 3 PID: 2182 Comm: kworker/3:1 Not tainted 4.0.0-10545-gb9bb6fb #204
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Workqueue: events flush_to_ldisc
8162a0c7 88011f583e88 814e6ba0 0002
88011f583ed8 88011f583ec8 8104d095 88011f583eb8
0003 0001 0001
Call Trace:
IRQ [814e6ba0] dump_stack+0x4f/0x7b
[8104d095] warn_slowpath_common+0x85/0xc0
[8104d146] warn_slowpath_fmt+0x46/0x50
[810bd2a9] can_stop_full_tick+0xb9/0x290
[810bd9ed] tick_nohz_irq_exit+0x8d/0xb0
[810511c5] irq_exit+0xc5/0x130
[814f180a] smp_apic_timer_interrupt+0x4a/0x60
[814eff5e] apic_timer_interrupt+0x6e/0x80
EOI [814ee5d1] ? _raw_spin_unlock_irqrestore+0x31/0x60
[8108bbc8] __wake_up+0x48/0x60
[8134836c] n_tty_receive_buf_common+0x49c/0xba0
[8134a6bf] ? tty_ldisc_ref+0x1f/0x70
[81348a84] n_tty_receive_buf2+0x14/0x20
[8134b390] flush_to_ldisc+0xe0/0x120
[81064d05] process_one_work+0x1d5/0x540
[81064c81] ? process_one_work+0x151/0x540
[81065191] worker_thread+0x121/0x470
[81065070] ? process_one_work+0x540/0x540
[8106b4df] kthread+0xef/0x110
[8106b3f0] ? __kthread_parkme+0xa0/0xa0
[814ef4f2] ret_from_fork+0x42/0x70
[8106b3f0] ? __kthread_parkme+0xa0/0xa0
---[ end trace 06e3507544a38866 ]---
However, it turns out that kvmclock does provide a stable
sched_clock callback. So, let the scheduler know this which
in turn makes NOHZ_FULL work in the guest.
Signed-off-by: Marcelo Tosatti mtosa...@redhat.com
Signed-off-by: Luiz Capitulino lcapitul...@redhat.com
---
PS: Original author of this patch is Marcelo. I did most of the
testing and backported it to an older real-time kernel tree. Works
like a charm.
arch/x86/kernel/kvmclock.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 42caaef..4e03921 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -24,6 +24,7 @@
#include linux/percpu.h
#include linux/hardirq.h
#include linux/memblock.h
+#include linux/sched.h
#include asm/x86_init.h
#include asm/reboot.h
@@ -265,6 +266,8 @@ void __init kvmclock_init(void)
if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
+
+ set_sched_clock_stable();
}
int __init kvm_setup_vsyscall_timeinfo(void)
--
1.9.3
--
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Ping?
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