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

[Wanpeng Li]

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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