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Subject: Re: [PATCH v4 1/2] x86/paravirt: Change vcp_is_preempted() arg type
 to long
To: Peter Zijlstra <peterz@infradead.org>
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From: Waiman Long <longman@redhat.com>
Organization: Red Hat
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Date: Thu, 16 Feb 2017 16:02:57 -0500
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On 02/16/2017 11:09 AM, Peter Zijlstra wrote:
> On Wed, Feb 15, 2017 at 04:37:49PM -0500, Waiman Long wrote:
>> The cpu argument in the function prototype of vcpu_is_preempted()
>> is changed from int to long. That makes it easier to provide a better
>> optimized assembly version of that function.
>>
>> For Xen, vcpu_is_preempted(long) calls xen_vcpu_stolen(int), the
>> downcast from long to int is not a problem as vCPU number won't exceed
>> 32 bits.
>>
> Note that because of the cast in PVOP_CALL_ARG1() this patch is
> pointless.
>
> Then again, it doesn't seem to affect code generation, so why not. Takes
> away the reliance on that weird cast.

I add this patch because I am a bit uneasy about clearing the upper 32
bits of rdi and assuming that the compiler won't have a previous use of
those bits. It gives me peace of mind.

Cheers,
Longman