On 05/15/2014 11:39 AM, Dongsheng Yang wrote:
As shown in 'man virsh' about schedinfo:
Note: The cpu_shares parameter has a valid value range of 0-262144; Negative values are wrapped to positive, and larger values are capped at the maximum. Therefore, -1 is a useful shorthand for 262144. On the Linux kernel, the values 0 and 1 are automatically converted to a minimal value of 2. it works well with --live, but not with --config.
Example: # virsh schedinfo rhel7-ful --set cpu_shares=0 --config Scheduler : posix cpu_shares : 0 vcpu_period : 0 vcpu_quota : 0 emulator_period: 0 emulator_quota : 0 cpu_shares is 0 rather than expected 2.
What's worse, when we start it again, it is the default value of cpu_shares 1024.
Because when we set the value of cpu_shares, when flag is --live, write the value into cgroup/cpu.shares. Then it will convert the value into the range of [2, 262144]. When flag is --config, we set the value into vmdef immidiately and 0 means no settting for cpu_shares. When we start vm again, libvirt use default value(1024) for it.
commit bdffab0d5c52d31bd71422b0b69665efb6650953 Author: Ján Tomko <jtomko@redhat.com> CommitDate: 2014-03-26 10:10:02 +0100 Treat zero cpu shares as a valid value changed this behavior. After this commit, if you set cpu_shares to 0 via schedinfo --config, the 0 will be written in the XML and used on domain startup. To use the default value, the <shares> element needs to be removed from the XML before restarting the domain, this cannot be currently done via 'virsh schedinfo'. Jan