[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 13/13] tools/libxl: Add 'vtsc_khz' option to set guest TSC rate
On 29/09/15 11:28, Ian Campbell wrote: > On Tue, 2015-09-29 at 11:24 +0100, Andrew Cooper wrote: >> 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. > Right. If it happens to come for free as a side effect of making it work > for migration then fine. > > But it seems to me that tsc rate could/should be in the hypervisors save > blob and require no interaction with the toolstack once it is latched when > the domain is built. There are a lot of blobs which fall into this category. Others are cpuid policy and guest-MSRs. I have a longterm plan to fix them, which is under very slow progress. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |