Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function

[Waiman Long <longman@xxxxxxxxxx>]

On 02/13/2017 05:53 AM, Peter Zijlstra wrote:
> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
>> That way we'd end up with something like:
>>
>> asm("
>> push %rdi;
>> movslq %edi, %rdi;
>> movq __per_cpu_offset(,%rdi,8), %rax;
>> cmpb $0, %[offset](%rax);
>> setne %al;
>> pop %rdi;
>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct 
>> steal_time, preempted)));
>>
>> And if we could get rid of the sign extend on edi we could avoid all the
>> push-pop nonsense, but I'm not sure I see how to do that (then again,
>> this asm foo isn't my strongest point).
> Maybe:
>
> movsql %edi, %rax;
> movq __per_cpu_offset(,%rax,8), %rax;
> cmpb $0, %[offset](%rax);
> setne %al;
>
> ?

Yes, that looks good to me.

Cheers,
Longman


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