TSC offset support for Xen
Bug #1160378 reported by
Stefan Bader
This bug affects 2 people
Affects | Status | Importance | Assigned to | Milestone | |
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xen (Ubuntu) |
Fix Released
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Wishlist
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Stefan Bader |
Bug Description
TSC is only writable via MSR 0x10 which is a moving target. TSC offset timer feature will provide a new MSR 0x3b that exposes the "Thread Offset" directly. So, RDTSC result = Core TSC + Core Offset + Thread Offset. This allows system software to avoid barriers when writing the TSC.
We will expose TSC offset timer feature into guest, and try to see whether Xen could make use this feature itself.
Upstream Schedule: Xen 4.3
Implemented by the following patches in upstream Xen git repository:
6e03363 x86: Implement TSC adjust feature for HVM guest
e35cd2c x86: Save/restore TSC adjust during HVM guest migration
6fd5f43 x86: Expose TSC adjust to HVM guest
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Tested to show no regressions without TSC adjust support (no hardware with support available, yet).