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Date:   Thu, 16 Feb 2017 16:02:57 -0500
From:   Waiman Long <>
To:     Peter Zijlstra <>
Cc:     Jeremy Fitzhardinge <>,
        Chris Wright <>,
        Alok Kataria <>,
        Rusty Russell <>,
        Ingo Molnar <>,
        Thomas Gleixner <>,
        "H. Peter Anvin" <>,,,,,,,
        Pan Xinhui <>,
        Paolo Bonzini <>,
        Radim Krčmář <>,
        Boris Ostrovsky <>,
        Juergen Gross <>
Subject: Re: [PATCH v4 1/2] x86/paravirt: Change vcp_is_preempted() arg type
 to long

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.


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