Re: KVM slow LAMP guest

["\"C. Bröcker\"" <c.brocker@intercollect.com>]

On 14-7-2015 19:16, David Matlack wrote:
> (adding back the kvm mailing list)
>
> On Tue, Jul 14, 2015 at 1:12 AM, "C. Bröcker"
> <c.brocker@intercollect.com> 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@google.com>
>>>> wrote:
>>>>> On Thu, Jun 18, 2015 at 1:25 AM, Hansa <forums@logic-q.nl> 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
Sorry David.
That is not an option. It's a production server on 2.6 kernel. 4.0 kernel is not in Base repos and I don't know which impact installing the newer kernel version will have on this server. Any other options?