Re: [PATCH] KVM: emulator: do not needlesly sync registers from emulator ctxt to vcpu

[Avi Kivity <avi@redhat.com>]

On 03/30/2011 02:12 PM, Avi Kivity wrote:
> On 03/30/2011 01:43 PM, Gleb Natapov wrote:
>> >
>> >  The patch saves copying of 256 bytes on each MMIO/PIO read. It may 
>> not
>> >  save a lot comparing to time it takes to do one MMIO to userspace, 
>> but
>> >  do 1 million of those and you saved a lot of CPU cycles. I do not 
>> think
>> >  we should abandon the optimization so easily. Unfortunately I 
>> can't run
>> >  perf on 2.6.38 kernel right now. It gives me strange errors and 
>> when it
>> >  doesn't it makes kernel OOPS.
>> >
>> After reboot perf started to work. I ran modified emulator.flat unit
>> test. It was modified to run test_cmps() in an endless loop.
>>
>> Without patch:
>> 1.71%  qemu-system-x86  [kvm]                 [k] 
>> x86_emulate_instruction
>> 1.51%  qemu-system-x86  [kvm]                 [k] 
>> x86_emulate_instruction
>> 1.68%  qemu-system-x86  [kvm]                 [k] 
>> x86_emulate_instruction
>>
>> With patch:
>> 0.84%  qemu-system-x86  [kvm]                 [k] 
>> x86_emulate_instruction
>> 0.96%  qemu-system-x86  [kvm]                 [k] 
>> x86_emulate_instruction
>> 0.89%  qemu-system-x86  [kvm]                 [k] 
>> x86_emulate_instruction
>>
>
> Well, that is probably significant.
>

Please rebase the patch after sse-mmio goes in.

-- 
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