Re: KVM slow LAMP guest

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(adding back the kvm mailing list)

On Tue, Jul 14, 2015 at 1:12 AM, "C. Bröcker"
<c.brocker@xxxxxxxxxxxxxxxx> wrote:
> On 14-7-2015 10:04, Hansa wrote:
>>
>> On 13-7-2015 20:57, David Matlack wrote:
>>>
>>> On Thu, Jun 18, 2015 at 10:26 AM, David Matlack <dmatlack@xxxxxxxxxx>
>>> wrote:
>>>>
>>>> On Thu, Jun 18, 2015 at 1:25 AM, Hansa <forums@xxxxxxxxxx> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I have a LAMP server as guest in KVM. Whenever the server is idle for
>>>>> some
>>>>> time it takes about 30 seconds to load a Wordpress site.
>>>>> If the server is not idle the site shows up in max 5 seconds. I've
>>>>> already
>>>>> turned of power management in the guest by passing
>>>>>
>>>>>      GRUB_CMDLINE_LINUX_DEFAULT="apm=off"
>>>>>
>>>>> in /etc/default/grub. This has no effect.
>>>>> Does KVM do some power management on guests? If so, how do I turn this
>>>>> off
>>>>> for my LAMP guest?
>>>>
>>>> KVM doesn't do any power management of guests. But if everything is idle
>>>> on
>>>> the host (including your guest), then host power management could kick
>>>> in.
>>>> Have you tried playing with host pm?
>>>>
>>>> Could you try running your workload with the guest kernel parameter
>>>> "idle=poll"
>>>> and let me know the performance?
>>>>
>>>> Also, if you are running Linux 4.0 or later on the host, could you try
>>>> running
>>>> your workload with the KVM module parameter "halt_poll_ns=500000"?
>>>
>>> Hansa-- Did you ever get a chance to run your workload with these
>>> changes?
>>
>> Hi David,
>>
>> Sorry I didn't respond to your mail earlier and nice of you to check back.
>> To be honest no I haven't. To much work overload on my side. I've just added
>> the idle=poll to the guests' grub and rebooted the server. I'll let it run a
>> few day's to check if it helps. Btw: I'm running 2.6 linux kernel here so
>> I'm not sure if I can add the "halt_poll_ns" param to KVM.
>>
>> Best, Hansa
>
> Wow! That makes real difference!
> The site was never that fast! Although CPU load is constantly on 100% any
> chance I can tweak this param? And is there a similar param for Windows
> guests?

Since idle=poll gave a noticeable improvement, your workload is a good
candidate for halt_poll_ns. This is a host KVM module parameter. It will
give you a similar speedup, it will work independent of your guest os,
and won't peg your cpu usage at 100% during periods of no activity. If
you don't have halt_poll_ns available (your host kernel older than 4.0),
is upgrading to a newer kernel or backporting the patch [1] an option?

I'm not sure of any more guest params you can tweak (linux or windows), but
I'll let you know if I come up with anything.

[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f7819512996361280b86259222456fcf15aad926
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