On 15/03/21 23:31, Jing Zhang wrote:
We are considering about how to create the file descriptor. It might be risky to create an extra fd for every vCPU. It will easily hit the fd limit for the process or the system for machines running a ton of small VMs.
You already have a file descriptor for every vCPU, but I agree that having twice as many is not very good.
Looks like creating an extra file descriptor for every VM is a better option. And then we can check per vCPU stats through Ioctl of this VM fd by passing the vCPU index.
The file descriptor idea is not really infeasible I think (not just because the # of file descriptors is "only" doubled, but also because most of the time I think you'd only care of per-VM stats).
If you really believe it's not usable for you, you can use two ioctls to fill the description and the data respectively (i.e. ioctl(fd, KVM_GET_STATS_{DESCRIPTION,VALUES}, pdata) using the same layout as below. If called with NULL argument, the ioctl returns how much data they will fill in.
The (always zero) global flags can be replaced by the value returned by KVM_CHECK_EXTENSION.
The number of statistics can be obtained by ioctl(fd, KVM_GET_STATS_VALUES, NULL), just divide the returned value by 8.
Paolo
4 bytes flags (always zero) 4 bytes number of statistics 4 bytes offset of the first stat description 4 bytes offset of the first stat value stat descriptions: - 4 bytes for the type (for now always zero: uint64_t) - 4 bytes for the flags (for now always zero) - length of name - name statistics in 64-bit format
