Messages in this thread | | | Date | Fri, 30 Jan 2015 16:10:27 +0100 | From | Paolo Bonzini <> | Subject | Re: [PATCH 7/8] KVM: x86: avoid logical_map when it is invalid |
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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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