* [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
@ 2014-02-18 2:38 Zhanghaoyu (A)
2014-02-18 10:38 ` Michael S. Tsirkin
0 siblings, 1 reply; 9+ messages in thread
From: Zhanghaoyu (A) @ 2014-02-18 2:38 UTC (permalink / raw)
To: qemu-devel@nongnu.org, KVM, Paolo Bonzini, Gleb Natapov,
Michael S. Tsirkin, Avi Kivity, Eric Blake
Cc: chenliang (T), Huangweidong (C), Zhanghaoyu (A), Luonengjun,
Gonglei (Arei), Gaowei (UVP)
Hi, all
The VM will get stuck for a while(about 6s for a VM with 20GB memory) when attaching a pass-through PCI card to the non-pass-through VM for the first time.
The reason is that the host will build the whole VT-d GPA->HPA DMAR page-table, which needs a lot of time, and during this time, the qemu_global_mutex
lock is hold by the main-thread, if the vcpu thread IOCTL return, it will be blocked to waiting main-thread to release the qemu_global_mutex lock,
so the VM got stuck.
The race between qemu-main-thread and vcpu-thread is shown as below,
QEMU-main-thread vcpu-thread
| |
qemu_mutex_lock_iothread qemu_mutex_lock(&qemu_global_mutex)
| |
+----loop- ->+ +----loop---->+
| | | |
| qemu_mutex_unlock_iothread | qemu_mutex_unlock_iothread
| | | |
| poll | kvm_vcpu_ioctl(KVM_RUN)
| | | |
| qemu_mutex_lock_iothread | |
| | | |
--------------------------------------------------------------------------------------
| | | qemu_mutex_lock_iothread
| kvm_device_pci_assign | |
| | | blocked to waiting main-thread to release the qemu lock
| about 6 sec for 20GB memory | |
| | | |
+------------+ +-------------+
Any advises?
Thanks,
Zhang Haoyu
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
2014-02-18 2:38 [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time Zhanghaoyu (A)
@ 2014-02-18 10:38 ` Michael S. Tsirkin
2014-02-18 10:42 ` Paolo Bonzini
2014-02-18 10:59 ` Zhanghaoyu (A)
0 siblings, 2 replies; 9+ messages in thread
From: Michael S. Tsirkin @ 2014-02-18 10:38 UTC (permalink / raw)
To: Zhanghaoyu (A)
Cc: chenliang (T), Avi Kivity, Huangweidong (C), KVM, Gleb Natapov,
Luonengjun, qemu-devel@nongnu.org, Gonglei (Arei), Paolo Bonzini,
Gaowei (UVP)
On Tue, Feb 18, 2014 at 02:38:40AM +0000, Zhanghaoyu (A) wrote:
> Hi, all
>
> The VM will get stuck for a while(about 6s for a VM with 20GB memory) when attaching a pass-through PCI card to the non-pass-through VM for the first time.
> The reason is that the host will build the whole VT-d GPA->HPA DMAR page-table, which needs a lot of time, and during this time, the qemu_global_mutex
> lock is hold by the main-thread, if the vcpu thread IOCTL return, it will be blocked to waiting main-thread to release the qemu_global_mutex lock,
> so the VM got stuck.
> The race between qemu-main-thread and vcpu-thread is shown as below,
>
> QEMU-main-thread vcpu-thread
> | |
> qemu_mutex_lock_iothread qemu_mutex_lock(&qemu_global_mutex)
> | |
> +----loop- ->+ +----loop---->+
> | | | |
> | qemu_mutex_unlock_iothread | qemu_mutex_unlock_iothread
> | | | |
> | poll | kvm_vcpu_ioctl(KVM_RUN)
> | | | |
> | qemu_mutex_lock_iothread | |
> | | | |
> --------------------------------------------------------------------------------------
> | | | qemu_mutex_lock_iothread
> | kvm_device_pci_assign | |
> | | | blocked to waiting main-thread to release the qemu lock
> | about 6 sec for 20GB memory | |
> | | | |
> +------------+ +-------------+
>
>
> Any advises?
>
> Thanks,
> Zhang Haoyu
What if you detach and re-attach?
Is it fast then?
If yes this means the issue is COW breaking that occurs
with get_user_pages, not translation as such.
Try hugepages with prealloc - does it help?
--
MST
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
2014-02-18 10:38 ` Michael S. Tsirkin
@ 2014-02-18 10:42 ` Paolo Bonzini
2014-02-18 10:51 ` Michael S. Tsirkin
2014-02-18 11:17 ` Zhanghaoyu (A)
2014-02-18 10:59 ` Zhanghaoyu (A)
1 sibling, 2 replies; 9+ messages in thread
From: Paolo Bonzini @ 2014-02-18 10:42 UTC (permalink / raw)
To: Michael S. Tsirkin, Zhanghaoyu (A)
Cc: chenliang (T), Avi Kivity, Huangweidong (C), KVM, Gleb Natapov,
Luonengjun, qemu-devel@nongnu.org, Gonglei (Arei), Gaowei (UVP)
Il 18/02/2014 11:38, Michael S. Tsirkin ha scritto:
> What if you detach and re-attach?
> Is it fast then?
> If yes this means the issue is COW breaking that occurs
> with get_user_pages, not translation as such.
> Try hugepages with prealloc - does it help?
I agree it's either COW breaking or (similarly) locking pages that the
guest hasn't touched yet.
You can use prealloc or "-rt mlock=on" to avoid this problem.
Paolo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
2014-02-18 10:42 ` Paolo Bonzini
@ 2014-02-18 10:51 ` Michael S. Tsirkin
2014-02-18 11:05 ` Paolo Bonzini
2014-02-18 11:17 ` Zhanghaoyu (A)
1 sibling, 1 reply; 9+ messages in thread
From: Michael S. Tsirkin @ 2014-02-18 10:51 UTC (permalink / raw)
To: Paolo Bonzini
Cc: chenliang (T), Avi Kivity, Huangweidong (C), Gleb Natapov, KVM,
Zhanghaoyu (A), Luonengjun, qemu-devel@nongnu.org, Gonglei (Arei),
Gaowei (UVP)
On Tue, Feb 18, 2014 at 11:42:19AM +0100, Paolo Bonzini wrote:
> Il 18/02/2014 11:38, Michael S. Tsirkin ha scritto:
> >What if you detach and re-attach?
> >Is it fast then?
> >If yes this means the issue is COW breaking that occurs
> >with get_user_pages, not translation as such.
> >Try hugepages with prealloc - does it help?
>
> I agree it's either COW breaking or (similarly) locking pages that
> the guest hasn't touched yet.
>
> You can use prealloc or "-rt mlock=on" to avoid this problem.
>
> Paolo
Or the new shared flag - IIRC shared VMAs don't do COW either.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
2014-02-18 10:51 ` Michael S. Tsirkin
@ 2014-02-18 11:05 ` Paolo Bonzini
2014-02-18 11:16 ` Michael S. Tsirkin
2014-02-24 11:38 ` Zhanghaoyu (A)
0 siblings, 2 replies; 9+ messages in thread
From: Paolo Bonzini @ 2014-02-18 11:05 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: chenliang (T), Avi Kivity, Huangweidong (C), Gleb Natapov, KVM,
Zhanghaoyu (A), Luonengjun, qemu-devel@nongnu.org, Gonglei (Arei),
Gaowei (UVP)
Il 18/02/2014 11:51, Michael S. Tsirkin ha scritto:
>> > I agree it's either COW breaking or (similarly) locking pages that
>> > the guest hasn't touched yet.
>> >
>> > You can use prealloc or "-rt mlock=on" to avoid this problem.
>> >
>> > Paolo
> Or the new shared flag - IIRC shared VMAs don't do COW either.
Only if the problem isn't locking and zeroing of untouched pages (also,
it is not upstream is it?).
Can you make a profile with perf?
Paolo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
2014-02-18 11:05 ` Paolo Bonzini
@ 2014-02-18 11:16 ` Michael S. Tsirkin
2014-02-24 11:38 ` Zhanghaoyu (A)
1 sibling, 0 replies; 9+ messages in thread
From: Michael S. Tsirkin @ 2014-02-18 11:16 UTC (permalink / raw)
To: Paolo Bonzini
Cc: chenliang (T), Avi Kivity, Huangweidong (C), Gleb Natapov, KVM,
Zhanghaoyu (A), Luonengjun, qemu-devel@nongnu.org, Gonglei (Arei),
Gaowei (UVP)
On Tue, Feb 18, 2014 at 12:05:19PM +0100, Paolo Bonzini wrote:
> Il 18/02/2014 11:51, Michael S. Tsirkin ha scritto:
> >>> I agree it's either COW breaking or (similarly) locking pages that
> >>> the guest hasn't touched yet.
> >>>
> >>> You can use prealloc or "-rt mlock=on" to avoid this problem.
> >>>
> >>> Paolo
> >Or the new shared flag - IIRC shared VMAs don't do COW either.
>
> Only if the problem isn't locking and zeroing of untouched pages
> (also, it is not upstream is it?).
No but it's a small patch - part of vhost user patchset.
> Can you make a profile with perf?
>
> Paolo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
2014-02-18 11:05 ` Paolo Bonzini
2014-02-18 11:16 ` Michael S. Tsirkin
@ 2014-02-24 11:38 ` Zhanghaoyu (A)
1 sibling, 0 replies; 9+ messages in thread
From: Zhanghaoyu (A) @ 2014-02-24 11:38 UTC (permalink / raw)
To: Paolo Bonzini, Michael S. Tsirkin
Cc: chenliang (T), Avi Kivity, Huangweidong (C), KVM, Gleb Natapov,
Luonengjun, qemu-devel@nongnu.org, Gonglei (Arei), Gaowei (UVP)
>>> > I agree it's either COW breaking or (similarly) locking pages that
>>> > the guest hasn't touched yet.
>>> >
>>> > You can use prealloc or "-rt mlock=on" to avoid this problem.
>>> >
>>> > Paolo
>> Or the new shared flag - IIRC shared VMAs don't do COW either.
>
>Only if the problem isn't locking and zeroing of untouched pages (also, it is not upstream is it?).
>
>Can you make a profile with perf?
>
"-rt mlock=on" option is not set， perf top -p <qemu pid> result:
21699 root 20 0 24.2g 24g 5312 S 0 33.8 0:24.39 qemu-system-x8
PerfTop: 95 irqs/sec kernel:17.9% us: 1.1% guest kernel:47.4% guest us:32.6% exact: 0.0% [1000Hz cycles], (target_pid: 15950)
----------------------------------------------------------------------------
samples pcnt function DSO
_______ _____ _____________________________________ ___________
2984.00 77.8% clear_page_c [kernel]
135.00 3.5% gup_huge_pmd [kernel]
134.00 3.5% pfn_to_dma_pte [kernel]
83.00 2.2% __domain_mapping [kernel]
63.00 1.6% update_memslots [kvm]
59.00 1.5% prep_new_page [kernel]
50.00 1.3% get_user_pages_fast [kernel]
45.00 1.2% up_read [kernel]
42.00 1.1% down_read [kernel]
38.00 1.0% gup_pud_range [kernel]
34.00 0.9% kvm_clear_async_pf_completion_queue [kvm]
18.00 0.5% intel_iommu_map [kernel]
16.00 0.4% _cond_resched [kernel]
16.00 0.4% gfn_to_hva [kvm]
15.00 0.4% kvm_set_apic_base [kvm]
15.00 0.4% load_vmcs12_host_state [kvm_intel]
14.00 0.4% clear_huge_page [kernel]
7.00 0.2% intel_iommu_iova_to_phys [kernel]
6.00 0.2% is_error_pfn [kvm]
6.00 0.2% iommu_map [kernel]
6.00 0.2% native_write_msr_safe [kernel]
5.00 0.1% find_vma [kernel]
"-rt mlock=on" option is set， perf top -p <qemu pid> result:
PerfTop: 326 irqs/sec kernel:17.5% us: 2.8% guest kernel:37.4% guest us:42.3% exact: 0.0% [1000Hz cycles], (target_pid: 25845)
----------------------------------------------------------------------------
samples pcnt function DSO
_______ _____ _____________________________________ ___________
182.00 17.5% pfn_to_dma_pte [kernel]
178.00 17.1% gup_huge_pmd [kernel]
91.00 8.8% __domain_mapping [kernel]
71.00 6.8% update_memslots [kvm]
65.00 6.3% gup_pud_range [kernel]
62.00 6.0% get_user_pages_fast [kernel]
52.00 5.0% kvm_clear_async_pf_completion_queue [kvm]
50.00 4.8% down_read [kernel]
37.00 3.6% up_read [kernel]
26.00 2.5% intel_iommu_map [kernel]
20.00 1.9% native_write_msr_safe [kernel]
16.00 1.5% gfn_to_hva [kvm]
14.00 1.3% load_vmcs12_host_state [kvm_intel]
8.00 0.8% find_busiest_group [kernel]
8.00 0.8% _raw_spin_lock [kernel]
8.00 0.8% hrtimer_interrupt [kernel]
8.00 0.8% intel_iommu_iova_to_phys [kernel]
7.00 0.7% iommu_map [kernel]
6.00 0.6% kvm_mmu_pte_write [kvm]
6.00 0.6% is_error_pfn [kvm]
5.00 0.5% kvm_set_apic_base [kvm]
5.00 0.5% clear_page_c [kernel]
5.00 0.5% iommu_iova_to_phys [kernel]
With "-rt mlock=on" option not set, when iommu_map, many new pages have to be allocated and cleared, the clear operation is expensive.
but no matter whether the "-rt mlock=on" option is set or not, the GPA->HPA DMAR page-table MUST be built, this operation is also expensive, about 1-2 sec needed for 25GB memory.
Thanks,
Zhang Haoyu
>Paolo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
2014-02-18 10:42 ` Paolo Bonzini
2014-02-18 10:51 ` Michael S. Tsirkin
@ 2014-02-18 11:17 ` Zhanghaoyu (A)
1 sibling, 0 replies; 9+ messages in thread
From: Zhanghaoyu (A) @ 2014-02-18 11:17 UTC (permalink / raw)
To: Paolo Bonzini, Michael S. Tsirkin
Cc: chenliang (T), Avi Kivity, Huangweidong (C), KVM, Gleb Natapov,
Luonengjun, qemu-devel@nongnu.org, Gonglei (Arei), Gaowei (UVP)
>> What if you detach and re-attach?
>> Is it fast then?
>> If yes this means the issue is COW breaking that occurs with
>> get_user_pages, not translation as such.
>> Try hugepages with prealloc - does it help?
>
>I agree it's either COW breaking or (similarly) locking pages that the guest hasn't touched yet.
>
>You can use prealloc or "-rt mlock=on" to avoid this problem.
>
It gets better if using "-rt mlock=on", but still cannot resolve the problem completely.
VT-d and EPT do not share the GPA->HPA page-table, still need to build VT-d GPA->HPA DMAR page-table,
Although the "-rt mlock=on" option guarantees that all of vm memory have been touched before attaching
the pass-through device, the building is faster, but which still need some time.
Thanks,
Zhang Haoyu
>Paolo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time
2014-02-18 10:38 ` Michael S. Tsirkin
2014-02-18 10:42 ` Paolo Bonzini
@ 2014-02-18 10:59 ` Zhanghaoyu (A)
1 sibling, 0 replies; 9+ messages in thread
From: Zhanghaoyu (A) @ 2014-02-18 10:59 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: chenliang (T), Avi Kivity, Huangweidong (C), KVM, Gleb Natapov,
Luonengjun, qemu-devel@nongnu.org, Gonglei (Arei), Paolo Bonzini,
Gaowei (UVP)
>> Hi, all
>>
>> The VM will get stuck for a while(about 6s for a VM with 20GB memory) when attaching a pass-through PCI card to the non-pass-through VM for the first time.
>> The reason is that the host will build the whole VT-d GPA->HPA DMAR
>> page-table, which needs a lot of time, and during this time, the
>> qemu_global_mutex lock is hold by the main-thread, if the vcpu thread IOCTL return, it will be blocked to waiting main-thread to release the qemu_global_mutex lock, so the VM got stuck.
>> The race between qemu-main-thread and vcpu-thread is shown as below,
>>
>> QEMU-main-thread vcpu-thread
>> | |
>> qemu_mutex_lock_iothread qemu_mutex_lock(&qemu_global_mutex)
>> | |
>> +----loop- ->+ +----loop---->+
>> | | | |
>> | qemu_mutex_unlock_iothread | qemu_mutex_unlock_iothread
>> | | | |
>> | poll | kvm_vcpu_ioctl(KVM_RUN)
>> | | | |
>> | qemu_mutex_lock_iothread | |
>> | | | |
>> --------------------------------------------------------------------------------------
>> | | | qemu_mutex_lock_iothread
>> | kvm_device_pci_assign | |
>> | | | blocked to waiting main-thread to release the qemu lock
>> | about 6 sec for 20GB memory | |
>> | | | |
>> +------------+ +-------------+
>>
>>
>> Any advises?
>>
>> Thanks,
>> Zhang Haoyu
>
>What if you detach and re-attach?
>Is it fast then?
Yes, because the VT-d GPA->HPA DMAR page-table has been built, no need to re-build it.
>If yes this means the issue is COW breaking that occurs with get_user_pages, not translation as such.
>Try hugepages with prealloc - does it help?
Yes, a bit help gained, but it cannot resolve the problem completely, the stuck still happened.
Thanks,
Zhang Haoyu
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2014-02-24 11:38 UTC | newest]
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2014-02-18 2:38 [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time Zhanghaoyu (A)
2014-02-18 10:38 ` Michael S. Tsirkin
2014-02-18 10:42 ` Paolo Bonzini
2014-02-18 10:51 ` Michael S. Tsirkin
2014-02-18 11:05 ` Paolo Bonzini
2014-02-18 11:16 ` Michael S. Tsirkin
2014-02-24 11:38 ` Zhanghaoyu (A)
2014-02-18 11:17 ` Zhanghaoyu (A)
2014-02-18 10:59 ` Zhanghaoyu (A)
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