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KVM: nVMX: track dirty state of non-shadowed VMCS fields

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VMCS12 fields that are not handled through shadow VMCS are rarely
written, and thus they are also almost constant in the vmcs02.  We can
thus optimize prepare_vmcs02 by skipping all the work for non-shadowed
fields in the common case.

This patch introduces the (pretty simple) tracking infrastructure; the
next patches will move work to prepare_vmcs02_full and save a few hundred
clock cycles per VMRESUME on a Haswell Xeon E5 system:

	                                before  after
	cpuid                           14159   13869
	vmcall                          15290   14951
	inl_from_kernel                 17703   17447
	outl_to_kernel                  16011   14692
	self_ipi_sti_nop                16763   15825
	self_ipi_tpr_sti_nop            17341   15935
	wr_tsc_adjust_msr               14510   14264
	rd_tsc_adjust_msr               15018   14311
	mmio-wildcard-eventfd:pci-mem   16381   14947
	mmio-datamatch-eventfd:pci-mem  18620   17858
	portio-wildcard-eventfd:pci-io  15121   14769
	portio-datamatch-eventfd:pci-io 15761   14831

(average savings 748, stdev 460).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
This commit is contained in:
Paolo Bonzini
2017-12-20 13:55:39 +01:00
committed by Radim Krčmář
parent c9e9deae76
commit 74a497fae7
2 changed files with 34 additions and 1 deletions
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6
arch/x86/kvm/vmx_shadow_fields.h
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@@ -17,6 +17,12 @@
* (e.g. force a sync if VM_INSTRUCTION_ERROR is modified
* by nested_vmx_failValid)
*
* When adding or removing fields here, note that shadowed
* fields must always be synced by prepare_vmcs02, not just
* prepare_vmcs02_full.
*/
/*
* Keeping the fields ordered by size is an attempt at improving
* branch prediction in vmcs_read_any and vmcs_write_any.
*/