On 29/09/15 11:13, Haozhong Zhang wrote: > On Tue, Sep 29, 2015 at 11:04:14AM +0100, Ian Campbell wrote: >> On Mon, 2015-09-28 at 15:13 +0800, Haozhong Zhang wrote: >>> This patch adds an option 'vtsc_khz' to allow users to set vcpu's TSC >>> rate in KHz. In the case that tsc_mode = 'default', the default value of >>> 'vtsc_khz' option is the host TSC rate which is used when 'vtsc_khz' >>> option is set to 0 or does not appear in the configuration. In all other >>> cases of tsc_mode, 'vtsc_khz' option is just ignored. >>> >>> Another purpose of adding this option is to keep vcpu's TSC rate across >>> guest reboot. In existing code, a new domain is created from the >>> configuration of the previous domain which was just rebooted. vcpu's TSC >>> rate is not stored in the configuration and the host TSC rate is the >>> used as vcpu's TSC rate. This works fine unless the previous domain was >>> migrated from another host machine with a different host TSC rate than >>> the current one. >> I understand why this is necessary over a migration, but why is it >> important to be able to retain the TSC rate across a reboot? What is the >> usecase there? >> > No usecase so far. Is 'making a virtual machine more like a physical > machine' reasonable here? (I suppose a physical machine retains TSC > rate across reboot)
There are situations such as altering firmware settings which can cause the TSC rate to differ across reboot. I don't see any reason to try and maintain it across VM reboots. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
