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

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.