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From: hpa@zytor.com
To: Waiman Long <longman@redhat.com>, 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>,
	"Rusty Russell" <rusty@rustcorp.com.au>,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	"Chris Wright" <chrisw@sous-sol.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	xen-devel@lists.xenproject.org,
	"Alok Kataria" <akataria@vmware.com>,
	"Thomas Gleixner" <tglx@linutronix.de>
Subject: Re: [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
Date: Mon, 13 Feb 2017 14:36:36 -0800	[thread overview]
Message-ID: <3A7771CA-4B1F-4BBD-9CB0-08680EFB2D11__25248.2880991467$1487025633$gmane$org@zytor.com> (raw)
In-Reply-To: <933ba8c6-4ebe-63e2-3c3a-2e5afef9269a@redhat.com>

On February 13, 2017 2:34:01 PM PST, Waiman Long <longman@redhat.com> wrote:
>On 02/13/2017 04:52 PM, Peter Zijlstra wrote:
>> On Mon, Feb 13, 2017 at 03:12:45PM -0500, Waiman Long wrote:
>>> 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.
>> I don't think that would be a problem, I very much doubt we declare
>more
>> than 4G worth of per-cpu variables in the kernel.
>>
>> In any case, use "e" or "Z" as constraint (I never quite know when to
>> use which). That are s32 and u32 displacement immediates resp. and
>> should fail compile with a semi-sensible failure if the displacement
>is
>> too big.
>>
>It is the address of &steal_time that will exceed the 32-bit limit.
>
>Cheers,
>Longman

That seems odd in the extreme?
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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  parent reply	other threads:[~2017-02-13 22:39 UTC|newest]

Thread overview: 69+ 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 15:43 ` Waiman Long
2017-02-10 16:19 ` Peter Zijlstra
2017-02-10 16:19 ` Peter Zijlstra
2017-02-10 16:19   ` Peter Zijlstra
2017-02-10 16:35   ` Waiman Long
2017-02-10 16:35     ` Waiman Long
2017-02-10 17:00     ` Waiman Long
2017-02-10 17:00     ` Waiman Long
2017-02-10 17:00       ` Waiman Long
2017-02-13 10:47       ` Peter Zijlstra
2017-02-13 10:47       ` Peter Zijlstra
2017-02-13 10:47         ` Peter Zijlstra
2017-02-13 10:53         ` Peter Zijlstra
2017-02-13 10:53         ` Peter Zijlstra
2017-02-13 10:53           ` Peter Zijlstra
2017-02-13 19:42           ` Waiman Long
2017-02-13 19:42           ` Waiman Long
2017-02-13 19:42           ` Waiman Long
2017-02-13 20:12             ` Waiman Long
2017-02-13 20:12               ` Waiman Long
2017-02-13 21:52               ` Peter Zijlstra
2017-02-13 21:52               ` Peter Zijlstra
2017-02-13 21:52                 ` Peter Zijlstra
2017-02-13 22:00                 ` hpa
2017-02-13 22:00                 ` hpa
2017-02-13 22:00                   ` hpa
2017-02-13 22:07                 ` hpa
2017-02-13 22:07                   ` hpa
2017-02-13 22:07                 ` hpa
2017-02-13 22:34                 ` Waiman Long
2017-02-13 22:34                 ` Waiman Long
2017-02-13 22:34                   ` Waiman Long
2017-02-13 22:36                   ` hpa
2017-02-13 22:36                     ` hpa
2017-02-13 22:36                   ` hpa [this message]
2017-02-14  9:39                   ` Peter Zijlstra
2017-02-14  9:39                   ` Peter Zijlstra
2017-02-14  9:39                     ` Peter Zijlstra
2017-02-14 14:46                     ` Waiman Long
2017-02-14 14:46                     ` Waiman Long
2017-02-14 14:46                       ` Waiman Long
2017-02-14 16:03                       ` Peter Zijlstra
2017-02-14 16:03                       ` Peter Zijlstra
2017-02-14 16:03                         ` Peter Zijlstra
2017-02-14 16:18                       ` [Xen-devel] " Andrew Cooper
2017-02-14 16:18                       ` Andrew Cooper
2017-02-14 16:18                       ` [Xen-devel] " Andrew Cooper
2017-02-13 20:12             ` Waiman Long
2017-02-13 20:06           ` hpa
2017-02-13 20:06             ` hpa
2017-02-13 21:57             ` Peter Zijlstra
2017-02-13 21:57               ` Peter Zijlstra
2017-02-13 21:57             ` Peter Zijlstra
2017-02-13 22:24             ` Waiman Long
2017-02-13 22:24               ` Waiman Long
2017-02-13 22:31               ` Peter Zijlstra
2017-02-13 22:31               ` Peter Zijlstra
2017-02-13 22:31                 ` Peter Zijlstra
2017-02-13 22:24             ` Waiman Long
2017-02-13 20:06           ` hpa
2017-02-13 19:41         ` Waiman Long
2017-02-13 19:41         ` Waiman Long
2017-02-13 19:41         ` Waiman Long
2017-02-10 16:35   ` Waiman Long
2017-02-10 16:22 ` Paolo Bonzini
2017-02-10 16:22 ` Paolo Bonzini
2017-02-10 16:22   ` Paolo Bonzini
  -- strict thread matches above, loose matches on Subject: below --
2017-02-10 15:43 Waiman Long

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