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Re: [Xen-devel] [PATCH] x86/svm: Improve code generation from cpu_has_svm_feature()


  • To: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 15 Mar 2019 16:22:59 +0000
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  • Cc: Brian Woods <brian.woods@xxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Fri, 15 Mar 2019 16:42:32 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 15/03/2019 15:59, Boris Ostrovsky wrote:
> On 3/15/19 11:23 AM, Andrew Cooper wrote:
>> Taking svm_feature_flags by pointer and using test_bit() results in generated
>> code which loads svm_feature_flags into a 32bit register, then does a bitwise
>> operation.
>>
>> The logic can be expressed in terms of a straight bitwise operation, 
>> resulting
>> in the following minor improvement.
>>
>>   add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-136 (-136)
>>   Function                                     old     new   delta
>>   svm_nested_features_on_efer_update           281     273      -8
>>   svm_create_vmcb                             1404    1388     -16
>>   svm_vmexit_handler                          6271    6239     -32
>>   start_svm                                    818     738     -80
>>   Total: Before=3347569, After=3347433, chg -0.00%
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>

I suppose you'd like me to fix up Oracle on commit? ;)

~Andrew

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