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From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Jeremy Fitzhardinge" <jeremy@goop.org>,
	"Chris Wright" <chrisw@sous-sol.org>,
	"Alok Kataria" <akataria@vmware.com>,
	"Rusty Russell" <rusty@rustcorp.com.au>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	linux-arch@vger.kernel.org, x86@kernel.org,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	xen-devel@lists.xenproject.org, kvm@vger.kernel.org,
	"Pan Xinhui" <xinhui.pan@linux.vnet.ibm.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Juergen Gross" <jgross@suse.com>
Subject: Re: [PATCH v4 1/2] x86/paravirt: Change vcp_is_preempted() arg type to long
Date: Thu, 16 Feb 2017 16:02:57 -0500	[thread overview]
Message-ID: <ac84bb22-6211-50e2-5b53-2f95c9142d76@redhat.com> (raw)
In-Reply-To: <20170216160930.GC6515@twins.programming.kicks-ass.net>

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

WARNING: multiple messages have this Message-ID (diff)
From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-arch@vger.kernel.org, "Juergen Gross" <jgross@suse.com>,
	"Jeremy Fitzhardinge" <jeremy@goop.org>,
	x86@kernel.org, kvm@vger.kernel.org,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Pan Xinhui" <xinhui.pan@linux.vnet.ibm.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	"Chris Wright" <chrisw@sous-sol.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	xen-devel@lists.xenproject.org,
	"Alok Kataria" <akataria@vmware.com>,
	"Thomas Gleixner" <tglx@linutronix.de>
Subject: Re: [PATCH v4 1/2] x86/paravirt: Change vcp_is_preempted() arg type to long
Date: Thu, 16 Feb 2017 16:02:57 -0500	[thread overview]
Message-ID: <ac84bb22-6211-50e2-5b53-2f95c9142d76@redhat.com> (raw)
In-Reply-To: <20170216160930.GC6515@twins.programming.kicks-ass.net>

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

  parent reply	other threads:[~2017-02-16 21:03 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-15 21:37 [PATCH v4 0/2] x86/kvm: Reduce vcpu_is_preempted() overhead Waiman Long
2017-02-15 21:37 ` [PATCH v4 1/2] x86/paravirt: Change vcp_is_preempted() arg type to long Waiman Long
2017-02-15 21:37 ` Waiman Long
2017-02-15 21:37 ` Waiman Long
2017-02-16 16:09   ` Peter Zijlstra
2017-02-16 16:09   ` Peter Zijlstra
2017-02-16 16:09     ` Peter Zijlstra
2017-02-16 21:02     ` Waiman Long
2017-02-16 21:02     ` Waiman Long [this message]
2017-02-16 21:02       ` Waiman Long
2017-02-17  9:42       ` Peter Zijlstra
2017-02-17  9:42         ` Peter Zijlstra
2017-02-17  9:42       ` Peter Zijlstra
2017-02-15 21:37 ` [PATCH v4 2/2] x86/kvm: Provide optimized version of vcpu_is_preempted() for x86-64 Waiman Long
2017-02-15 21:37 ` Waiman Long
2017-02-15 21:37   ` Waiman Long
2017-02-16 16:48   ` Peter Zijlstra
2017-02-16 16:48   ` Peter Zijlstra
2017-02-16 16:48     ` Peter Zijlstra
2017-02-16 21:00     ` Waiman Long
2017-02-16 21:00       ` Waiman Long
2017-02-16 21:00     ` Waiman Long

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