Looks like I saw the reason for that but I have no idea why this is happening.
Immediately after running "virsh start VM2" I saw on VM1 a swapper thread running for a lot of time causing this delay and another thing when I checked "top" before and after I saw a drop in a free RAM memory and increase in a SWAP available memory (both by ~100M). this explains why the swapper showed up. BUT how can you explain such behavior if I have totally isolated VMs running with 4G RAM each when on the HOST I have ~60G of free RAM space? Is it possible that both QEMUs try to allocate a shared memory region in HOSTs RAM that causes such interference ? Thanks, Yan From: Yadi [mailto:yadi...@windriver.com] Sent: Tuesday, July 26, 2016 12:24 PM To: qemu-discuss@nongnu.org; Yan Fridland Subject: Re: [Qemu-discuss] [problem]-starting a VM causes RT (latency) problem for application running on another VM On 2016年07月26日 15:48, Yan Fridland wrote: Hi Yadi, Thanks a lot for your comment. Actually I am doing emulator pin to the QEMU process in the XML: <vcpu placement='static'>3</vcpu> <cputune> <vcpupin vcpu='0' cpuset='1'/> <vcpupin vcpu='1' cpuset='2'/> <vcpupin vcpu='2' cpuset='3'/> <emulatorpin cpuset='8'/> <vcpusched vcpus='1-2' scheduler='fifo' priority='99'/> </cputune> BUT, looks like it doesn’t help. Is there any way to make ALL the related QEMU threads run within the scope of cores 1,2,3,8 ONLY in the above example? it is so wired, I have no better ways to handle it since I have no experienced the similar issue as your. so, just two suggestion for you: 1: check all qemu thread associated entries under cgroup filesystem, sure that cpusets are correctly set. 2: if 1 fails, it may means there is nothing left to do, ftrace for schduler. whatever result, let me know please. I am very interesting in the issue. Yadi Thanks, Yan From: Yadi [mailto:yadi...@windriver.com] Sent: Tuesday, July 26, 2016 6:12 AM To: Yan Fridland; qemu-discuss@nongnu.org<mailto:qemu-discuss@nongnu.org> Subject: Re: [Qemu-discuss] [problem]-starting a VM causes RT (latency) problem for application running on another VM On 2016年07月25日 23:03, Yan Fridland wrote: Hello All, Here is a problem I saw when I ran virsh start to a VM. I have 2VMs on a server when one of them is running a RT application and the other is in shut down state. Then I executed "virsh start" to the second VM and saw 2-3 seconds later a big latency problem in my RT application running on the first VM. I want to emphasize that the VMs use dedicated isolated cores of the server and I have the relevant configuration on the server and the vcpu pinning section of virsh xml. Can anyone tell me why I experience such behavior and how it can be resolved? I will highly appreciate your help. Thank you, Yan I am not very sure, but I suggest you to add emulatorpin in xml file, then see results. actually, all qemu associated process can use all processors via cgroup configure created by libvirt, https://libvirt.org/formatdomain.html#elementsCPUTuning
