From: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu, 27 Mar 2014 10:29:28 +0000 (+0100)
Subject: KVM: x86: avoid useless set of KVM_REQ_EVENT after emulation
X-Git-Tag: omap-for-v3.17/fixes-against-rc2~184^2~40
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6addfc42992be4b073c39137ecfdf4b2aa2d487f;p=pandora-kernel.git

KVM: x86: avoid useless set of KVM_REQ_EVENT after emulation

Despite the provisions to emulate up to 130 consecutive instructions, in
practice KVM will emulate just one before exiting handle_invalid_guest_state,
because x86_emulate_instruction always sets KVM_REQ_EVENT.

However, we only need to do this if an interrupt could be injected,
which happens a) if an interrupt shadow bit (STI or MOV SS) has gone
away; b) if the interrupt flag has just been set (other instructions
than STI can set it without enabling an interrupt shadow).

This cuts another 700-900 cycles from the cost of emulating an
instruction (measured on a Sandy Bridge Xeon: 1650-2600 cycles
before the patch on kvm-unit-tests, 925-1700 afterwards).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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