Date:	Sat, 29 Aug 2015 15:26:11 -0700
From:	Peter Kieser <peter@...ser.ca>
To:	Wanpeng Li <wanpeng.li@...mail.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	David Matlack <dmatlack@...gle.com>, kvm <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 0/3] KVM: Dynamic Halt-Polling

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:

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(-)
>>
>

-- 
Peter Kieser
604.338.9294 / peter@...ser.ca



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