Re: [libvirt] Performance about x-data-plane

On Thu, Dec 22, 2016 at 01:34:47AM -0500, Weiwei Jia wrote: > Hi, > > With QEMU x-data-plane, I find the performance has not been improved > very much. Please see following two settings. > > Setting 1: I/O thread in host OS (VMM) reads 4KB each time from disk > (8GB in total). Pin the I/O thread to pCPU 5 which will serve I/O > thread dedicatedly. I find the performance is around 250 MB/s. > > Setting 2: I/O thread in guest OS (VMM) reads 4KB each time from > virtual disk (8GB in total). Pin the I/O thread to vCPU 5 and pin vCPU > 5 thread to pCPU5 so that vCPU 5 handles this I/O thread dedicatedly > and pCPU5 serve vCPU5 dedicatedly. In order to keep vCPU5 not to be > idle, I also pin one cpu intensive thread (while (1) {i++}) on vCPU 5 > so that the I/O thread on it can be served without delay. For this > setting, I find the performance for this I/O thread is around 190 > MB/s. > > NOTE: For setting 2, I also pin the QEMU dedicated IOthread > (x-data-plane) in host OS to pCPU to handle I/O requests from guest OS > dedicatedly. > > I think for setting 2, the performance of I/O thread should be almost > the same as setting 1. I cannot understand why it is 60 MB/s lower > than setting 1. I am wondering whether there are something wrong with > my x-data-plane setting or virtio setting for VM. Would you please > give me some hints? Thank you. The x-data-plane option is obsolete and should not be used. You should use the modern iothread option instead, which is explicitly supported by libvirt XML. http://libvirt.org/formatdomain.html#elementsIOThreadsAllocation