linux-kernel - Re: [PATCH] pvclock: introduce seqcount-like API

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Date:	Thu, 9 Jun 2016 11:08:44 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Roman Kagan <rkagan@...tuozzo.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	Minfei Huang <mnghuan@...il.com>,
	Andrew Lutomirski <luto@...nel.org>
Subject: Re: [PATCH] pvclock: introduce seqcount-like API

On Thu, Jun 9, 2016 at 11:03 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
>
> On 09/06/2016 19:12, Andy Lutomirski wrote:
>> On Thu, Jun 9, 2016 at 6:45 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>>> On 09/06/2016 15:35, Roman Kagan wrote:
>>>> On Thu, Jun 09, 2016 at 02:47:54PM +0200, Paolo Bonzini wrote:
>>>>> On 09/06/2016 14:43, Roman Kagan wrote:
>>>> Has it landed in any public tree?  I'm unable to find any.  There
>>>> appears to be another version of the patch on the list, so I'm confused.
>>>
>>> I'm about to push it to kvm/master.
>>
>> Sorry for being slow.  I'm catching up.  In its current form, I don't
>> like this patch.  Please don't apply it.
>
> Sure, I was talking about Minfei's patches, not this one. :)  Of course
> I need ack for this one.
>
>> The problem is that this makes two significant changes at once:
>>
>> 1. Use the new version helpers.  I like that change.
>>
>> 2. Use __pvclock_read_cycles.  That should be separate, and it should
>> come with timing numbers in the changelog.
>
> __pvclock_read_cycles is pretty much the same as the code that is being
> inlined.  Thus the only change is that __pvclock_read_cycles is called
> inside the loop rather than outside, but the loop really is expected to
> never roll so why make a copy in the first place?

I feel like I had a reason, but I don't remember what it was.

--Andy