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