Re: [v4][PATCH 11/19] tools: introduce some new parameters to set rdm policy

From: "Chen, Tiejun" <tiejun.chen@intel.com>
To: George Dunlap <george.dunlap@eu.citrix.com>,
	Jan Beulich <jbeulich@suse.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Wei Liu <wei.liu2@citrix.com>,
	Ian Campbell <ian.campbell@citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [v4][PATCH 11/19] tools: introduce some new parameters to set rdm policy
Date: Mon, 06 Jul 2015 21:34:27 +0800	[thread overview]
Message-ID: <559A83E3.7040401@intel.com> (raw)
In-Reply-To: <5593EB53.5000601@eu.citrix.com>

I think we should go back here.

> I was involved in the design discussion, and from the very beginning I
> probably saw your plan but misunderstood it.  I wouldn't be surprised if
> some others didn't quite understand what they were agreeing to.
>
> This way of doing things is different than the way we do it with most
> other options relating to pci devices (e.g., pci_permissive,
> pci_msitranslate, pci_sieze, &c).  All of those options use a "default"
> semantic: the domain-wide setting takes effect only if it's not set
> locally.  If the syntax looks the same but the semantics is different,
> many people will be confused.  If we're going to have the domain-wide
> policy override the per-device policy, then the naming should make that
> clear; for instance, "override=(strict|relaxed|none)", or
> "strict_override=(1|0)".

Jan,

What about this?

This is involving our policy so please take a look at this as well.

George,

Actually we don't mean the domain-wide policy always override the 
per-device policy, or the per-device policy always override the 
per-device policy. Here we just take "strict" as the highest priority 
when it conflicts in two cases. As I said previously myself may not 
answer this very correctly but now I can recall or understand that one 
reason is that different devices can share one RMRR entry, so its 
possible that these two or more per-device policies are not same. So we 
need this particular rule which is not same as before. So I still prefer 
to keep our original implementation.

If I'm missing something or wrong, please Jan correct me.

Thanks
Tiejun

>
> I don't happen to think these "override" semantics are actually going to
> turn out to be that useful; I do think a "default" semantic would be
> useful.  But I'd be content if the name of the current setting were
> switched to "override" to make the semantics more clear.  We can always
> add in "default" at some later point if we really want.
>
>   -George
>