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 v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
Date: Mon, 13 Feb 2017 15:12:45 -0500 [thread overview]
Message-ID: <6f69b112-7ae4-bf8f-b767-29a68fd48632@redhat.com> (raw)
In-Reply-To: <3dc50409-60dd-ad47-f971-448191e66038@redhat.com>
On 02/13/2017 02:42 PM, Waiman Long wrote:
> 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
>
Sorry, I am going to take it back. The displacement or offset can only
be up to 32-bit. So we will still need to use at least one more
register, I think.
Cheers,
Longman
next prev parent reply other threads:[~2017-02-13 20:12 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-10 15:43 [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function Waiman Long
2017-02-10 16:19 ` Peter Zijlstra
2017-02-10 16:35 ` Waiman Long
2017-02-10 17:00 ` Waiman Long
2017-02-13 10:47 ` Peter Zijlstra
2017-02-13 10:53 ` Peter Zijlstra
2017-02-13 19:42 ` Waiman Long
2017-02-13 20:12 ` Waiman Long [this message]
2017-02-13 21:52 ` Peter Zijlstra
2017-02-13 22:00 ` hpa
2017-02-13 22:07 ` hpa
2017-02-13 22:34 ` Waiman Long
2017-02-13 22:36 ` hpa
2017-02-14 9:39 ` Peter Zijlstra
2017-02-14 14:46 ` Waiman Long
2017-02-14 16:03 ` Peter Zijlstra
2017-02-14 16:18 ` [Xen-devel] " Andrew Cooper
2017-02-13 20:06 ` hpa
2017-02-13 21:57 ` Peter Zijlstra
2017-02-13 22:24 ` Waiman Long
2017-02-13 22:31 ` Peter Zijlstra
2017-02-13 19:41 ` Waiman Long
2017-02-10 16:22 ` Paolo Bonzini
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