Re: [PATCH v4 0/3] KVM: Dynamic Halt-Polling

[Wanpeng Li]

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:

Thanks for the report. If Paolo's patch "kvm: add halt_poll_ns module 
parameter" is applied on your 3.18? Btw, do you test the linux guest?

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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