Ryan Boyce <ryanpboyc...@gmail.com> writes:
> Alex, > > I have another KVM/qemu related CPU question. I am hoping you will be so > kind as to answer again. I have a Dell Poweredge T430 server running a > single Intel Xeon E5-2603 v3 CPU with 6 cores. I have 6 VMs running CentOS > 7 via KVM. I am noticing some terrible host CPU performance when a VM runs > a simple process such as a recursive search on its file system. I see VM > CPU acting normally but the host CPU skyrockets to well over 100%. I have a > few ideas as to why this is but am hoping you might be able to point me in > the right direction. Thank you so much for your help! A lot will depend on caching and how much of your guest file-system is already in the host page cache. Otherwise you have a round-trip to make to load the blocks into RAM. However usually my first step is to run something like: perf top And see where the host is spending its time and go from there. > > Ryan > > On Wed, Jun 12, 2019 at 12:50 PM Ryan Boyce <ryanpboyc...@gmail.com> wrote: > >> Thank you my friend! >> >> On Wed, Jun 12, 2019 at 12:48 PM Alex Bennée <alex.ben...@linaro.org> >> wrote: >> >>> You've actually contacted the development list but I can answer the >>> question. >>> >>> QEMU is multi-threaded so there will be a thread per KVM based vCPU >>> (and also for TCG based vCPUs where MTTCG is enabled). There will also >>> be a number of additional threads created including at least one for >>> the main monitor thread and potentially additional threads for >>> servicing IO requests. So expect to see $SMP + 1 + n threads for each >>> QEMU instance. >>> >>> On Wed, 12 Jun 2019 at 16:32, Ryan Boyce <ryanpboyc...@gmail.com> wrote: >>> > >>> > Hi Stefan, >>> > >>> > I am a big fan of your blog! In relation to your blog post, >>> > >>> http://blog.vmsplice.net/2011/03/qemu-internals-big-picture-overview.html >>> , >>> > I have a question I am really hoping you can answer: >>> > >>> > When I start a VM, I see that the qemu-kvm processes start and run as >>> > "qemu-kvm..... -name "something1"...." >>> > My issue, though, is I see multiple processes running as "qemu-kvm..... >>> > -name "something1"...." and each of these processes has memory/cpu/disk >>> > mapped to it. >>> > Does qemu-kvm run VMs on a one-to-one VM-to-host process basis? Or does >>> > each virtual cpu on the guest get its own process on the host? >>> > For example, If I have a VM that has 4 virtual cpus, will I see 4 >>> processes >>> > (PIDs) on the host or should I see just see one for the VM itself. >>> > >>> > Any help you can give would be GREATLY appreciated. Thank you! >>> > >>> > Ryan >>> >>> >>> >>> -- >>> Alex Bennée >>> KVM/QEMU Hacker for Linaro >>> >> -- Alex Bennée