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

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Date:	Sun, 30 Aug 2015 06:21:28 +0800
From:	Wanpeng Li <wanpeng.li@...mail.com>
To:	Peter Kieser <peter@...ser.ca>
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

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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