On 30/01/2015 15:56, Radim Krčmář wrote:
> 2015-01-30 10:38+0100, Paolo Bonzini:
>> On 29/01/2015 22:48, Radim Krčmář wrote:
>>> + if (hweight8(new->mode) != 1)
>>
>> Better (more optimized):
>>
>> if (new->mode & (new->mode - 1))
>
> True, hweight needs to have X86_FEATURE_POPCNT to be efficient ...
>
> Do you know of a difference with it?
> new->mode & (new->mode - 1) | hweight8(new->mode) != 1
> lea -0x1(%rax),%edi | popcnt %edi,%eax
> test %eax,%edi | cmp $1,%eax
x & (x - 1) is really hweight8(new->mode) > 1. So if new->mode == 0 it
would have a different result.
>> Please add a comment to kvm_irq_delivery_to_apic_fast to explain what
>> you are doing.
>
> Would naming it kvm_apic_need_slow_delivery(), or something, be enough?
Or kvm_apic_map_valid() perhaps?
Paolo
>>> + if (hweight8(map->mode) != 1) {
>>> + /* Not deliverable with optimized map. */
>>> + ret = false;
>>> + goto out;
>>> + }
>>
>> Put this before the computation of cid and mda. The cid and mda are all
>> wrong with a mixed map, and the result of the "if" before is influenced
>> by the wrong cid. Fixed by patch 8, but better get it right here.
>
> Will do,
>
> thanks.
>
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