From: Chuck Lever <chuck.lever@oracle.com>
Subject: Re: [RFC,
	PATCH 04/35] svc: Add a max payload value to the transport
Date: Wed, 3 Oct 2007 11:18:25 -0400
Message-ID: <BD4C317A-01F3-4D2F-B486-1D280AE3EBFA@oracle.com>
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	<20071003110932.GN21388@sgi.com>
	<1191421613.1565.100.camel@trinity.ogc.int>
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Cc: neilb@suse.de, bfields@fieldses.org, nfs@lists.sourceforge.net,
	Greg Banks <gnb@sgi.com>
To: tom@opengridcomputing.com
In-Reply-To: <1191421613.1565.100.camel@trinity.ogc.int>
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On Oct 3, 2007, at 10:26 AM, Tom Tucker wrote:
> On Wed, 2007-10-03 at 21:09 +1000, Greg Banks wrote:
>> On Tue, Oct 02, 2007 at 11:28:08AM -0500, Tom Tucker wrote:
>
> [...snip...]
>
>>>
>>> The premise was that I didn't want a given thread peeking into some
>>> other processors memory, so anything needed from the class is copied
>>> into the svc_xprt structure when the transport instance is created.
>>
>> If I understand the code correctly, the only field in svc_xprt_class
>> that ever changes is the list_head used to add it to the global list,
>> which changes once when the transport module is loaded.  After that
>> all the svc_xprt_class cachelines will remain in shared state in all
>> CPUs' caches; it's effectively read-only.  Given that, there's little
>> to be concerned about.
>>
>>>
>>> Greg, help me here ;-)
>>
>> Sorry, I agree with Chuck :-/
>
> np, let's get it right. So the max_payload should remain in the
> svc_xprt_class structure.
>
> I see only one possible benefit of copying the svc_xprt_ops structure
> and that is that it saves one ptr de-reference when calling ops.  
> What's
> the consensus? Copy it, or keep a ptr?

My preference is not to copy it.

I'm not aware of any place in the kernel that copies the ops vector  
into each instance of an object, and I don't see that we have a  
strong motivation to implement something unique in this case.

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com


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