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SubjectRe: [PATCH v4 0/3] KVM: Dynamic Halt-Polling
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On 8/31/15 3:44 PM, Wanpeng Li wrote:
> On 8/30/15 6:26 AM, Peter Kieser wrote:
>> Thanks, Wanpeng. Applied this to Linux 3.18 and seeing much higher CPU
>> usage (200%) for qemu 2.4.0 process on a Windows 10 x64 guest. qemu
>> parameters:
>
> Interesting. I test this against latest kvm tree and stable qemu
> 2.0.0, 4 vCPUs on pCPU0(other pCPUs are offline to easy observe %C0
> and to avoid vCPUs schedule overhead influence). I just ignore the
> fluctuation and post the most common result of %C0 against the Windows
> 10 x86 guest.

s/x86/x64

>
> +-----------------+----------------+-----------------------+
> | | | |
> | w/o halt-poll | w/ halt-poll | dynamic(v4) halt-poll |
> +-----------------+----------------+-----------------------+
> | | | |
> | ~2.1% | ~3.0% | ~2.4% |
> +-----------------+----------------+-----------------------+
>
> Regards,
> Wanpeng Li
>
>>
>> qemu-system-x86_64 -enable-kvm -name arwan-20150704 -S -machine
>> pc-q35-2.2,accel=kvm,usb=off -cpu
>> Haswell,hv_time,hv_relaxed,hv_vapic,hv_spinlocks=0x1000 -m 8192
>> -realtime mlock=off -smp 4,sockets=4,cores=1,threads=1 -uuid
>> 7c2fc02d-2798-4fc9-ad04-db5f1af92723 -no-user-config -nodefaults
>> -chardev
>> socket,id=charmonitor,path=/var/lib/libvirt/qemu/arwan-20150704.monitor,server,nowait
>>
>> -mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime
>> -no-shutdown -boot strict=on -device
>> i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x1e -device
>> pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x1 -device
>> nec-usb-xhci,id=usb1,bus=pci.2,addr=0x4 -device
>> virtio-serial-pci,id=virtio-serial0,bus=pci.2,addr=0x5 -drive
>> file=/dev/mapper/crypt-arwan-20150704,if=none,id=drive-virtio-disk0,format=raw,cache=none,discard=unmap,aio=native
>>
>> -device
>> virtio-blk-pci,scsi=off,bus=pci.2,addr=0x3,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=2
>>
>> -drive
>> file=/usr/share/virtio-win/virtio-win.iso,if=none,media=cdrom,id=drive-sata0-0-2,readonly=on,format=raw
>>
>> -device
>> ide-cd,bus=ide.2,drive=drive-sata0-0-2,id=sata0-0-2,bootindex=1
>> -netdev tap,fds=31:32:33:34,id=hostnet0,vhost=on,vhostfds=35:36:37:38
>> -device
>> virtio-net-pci,guest_csum=off,guest_tso4=off,guest_tso6=off,mq=on,vectors=10,netdev=hostnet0,id=net0,mac=52:54:00:f3:6b:c4,bus=pci.2,addr=0x2
>>
>> -chardev
>> socket,id=charchannel0,path=/var/lib/libvirt/qemu/channel/target/arwan-20150704.org.qemu.guest_agent.0,server,nowait
>>
>> -device
>> virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
>>
>> -chardev spicevmc,id=charchannel1,name=vdagent -device
>> virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=com.redhat.spice.0
>>
>> -vnc 127.0.0.1:4 -device
>> qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vgamem_mb=16,bus=pcie.0,addr=0x1
>>
>> -device virtio-balloon-pci,id=balloon0,bus=pci.2,addr=0x1 -msg
>> timestamp=on
>>
>> I revert patch, qemu shows 17% CPU usage on host. Thoughts?
>>
>> -Peter
>>
>> On 2015-08-29 3:21 PM, Wanpeng Li wrote:
>>> Hi Peter,
>>> On 8/30/15 5:18 AM, Peter Kieser wrote:
>>>> Hi Wanpeng,
>>>>
>>>> Do I need to set any module parameters to use your patch, or should
>>>> halt_poll_ns automatically tune with just your patch series applied?
>>>>
>>>
>>> You don't need any module parameters.
>>>
>>> Regards,
>>> Wanpeng Li
>>>
>>>> Thanks.
>>>>
>>>> On 2015-08-27 2:47 AM, Wanpeng Li wrote:
>>>>> v3 -> v4:
>>>>> * bring back grow vcpu->halt_poll_ns when interrupt arrives and
>>>>> shrinks
>>>>> when idle VCPU is detected
>>>>>
>>>>> v2 -> v3:
>>>>> * grow/shrink vcpu->halt_poll_ns by *halt_poll_ns_grow or
>>>>> /halt_poll_ns_shrink
>>>>> * drop the macros and hard coding the numbers in the param
>>>>> definitions
>>>>> * update the comments "5-7 us"
>>>>> * remove halt_poll_ns_max and use halt_poll_ns as the max
>>>>> halt_poll_ns time,
>>>>> vcpu->halt_poll_ns start at zero
>>>>> * drop the wrappers
>>>>> * move the grow/shrink logic before "out:" w/ "if (waited)"
>>>>>
>>>>> v1 -> v2:
>>>>> * change kvm_vcpu_block to read halt_poll_ns from the vcpu
>>>>> instead of
>>>>> the module parameter
>>>>> * use the shrink/grow matrix which is suggested by David
>>>>> * set halt_poll_ns_max to 2ms
>>>>>
>>>>> There is a downside of halt_poll_ns since poll is still happen for
>>>>> idle
>>>>> VCPU which can waste cpu usage. This patchset add the ability to
>>>>> adjust
>>>>> halt_poll_ns dynamically, grows halt_poll_ns if an interrupt
>>>>> arrives and
>>>>> shrinks halt_poll_ns when idle VCPU is detected.
>>>>>
>>>>> There are two new kernel parameters for changing the halt_poll_ns:
>>>>> halt_poll_ns_grow and halt_poll_ns_shrink.
>>>>>
>>>>>
>>>>> Test w/ high cpu overcommit ratio, pin vCPUs, and the halt_poll_ns of
>>>>> halt-poll is the default 500000ns, the max halt_poll_ns of dynamic
>>>>> halt-poll is 2ms. Then watch the %C0 in the dump of Powertop tool.
>>>>> The test method is almost from David.
>>>>>
>>>>> +-----------------+----------------+-------------------+
>>>>> | | | |
>>>>> | w/o halt-poll | w/ halt-poll | dynamic halt-poll |
>>>>> +-----------------+----------------+-------------------+
>>>>> | | | |
>>>>> | ~0.9% | ~1.8% | ~1.2% |
>>>>> +-----------------+----------------+-------------------+
>>>>> The always halt-poll
>>>>> will increase ~0.9% cpu usage for idle vCPUs and the
>>>>> dynamic halt-poll drop it to ~0.3% which means that reduce the 67%
>>>>> overhead
>>>>> introduced by always halt-poll.
>>>>>
>>>>> Wanpeng Li (3):
>>>>> KVM: make halt_poll_ns per-VCPU
>>>>> KVM: dynamic halt_poll_ns adjustment
>>>>> KVM: trace kvm_halt_poll_ns grow/shrink
>>>>>
>>>>> include/linux/kvm_host.h | 1 +
>>>>> include/trace/events/kvm.h | 30 ++++++++++++++++++++++++++++
>>>>> virt/kvm/kvm_main.c | 50
>>>>> +++++++++++++++++++++++++++++++++++++++++++---
>>>>> 3 files changed, 78 insertions(+), 3 deletions(-)
>>>>
>>>
>>
>
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