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authorYunhong Jiang <yunhong.jiang@gmail.com>2016-06-13 14:20:01 -0700
committerYunhong Jiang <yunhong.jiang@linux.intel.com>2016-07-18 08:06:50 -0700
commitebcdab040619575a47ad19b18e7ed5c38d287336 (patch)
treed806a3a9443fcf29245e37aa0efc5f4a4de5230c /kernel/Kbuild
parentab9c81f473b3feff08f1e51428fbaf6a93d4896a (diff)
KVM: x86: support using the vmx preemption timer for tsc deadline timer
The VMX preemption timer can be used to virtualize the TSC deadline timer. The VMX preemption timer is armed when the vCPU is running, and a VMExit will happen if the virtual TSC deadline timer expires. When the vCPU thread is blocked because of HLT, KVM will switch to use an hrtimer, and then go back to the VMX preemption timer when the vCPU thread is unblocked. This solution avoids the complex OS's hrtimer system, and the host timer interrupt handling cost, replacing them with a little math (for guest->host TSC and host TSC->preemption timer conversion) and a cheaper VMexit. This benefits latency for isolated pCPUs. [A word about performance... Yunhong reported a 30% reduction in average latency from cyclictest. I made a similar test with tscdeadline_latency from kvm-unit-tests, and measured - ~20 clock cycles loss (out of ~3200, so less than 1% but still statistically significant) in the worst case where the test halts just after programming the TSC deadline timer - ~800 clock cycles gain (25% reduction in latency) in the best case where the test busy waits. I removed the VMX bits from Yunhong's patch, to concentrate them in the next patch - Paolo] Signed-off-by: Yunhong Jiang <yunhong.jiang@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Change-Id: I4aa1ecfa3463d1cbfb317511b45d2074b33d9b6f upstream-status: backport Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>
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