Re: [PATCH 4/5] iommu: introduce iommu_groups

From: Paul Durrant <Paul.Durrant@citrix.com>
To: 'Jan Beulich' <JBeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	"Tim (Xen.org)" <tim@xen.org>,
	George Dunlap <George.Dunlap@citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Ian Jackson <Ian.Jackson@citrix.com>
Subject: Re: [PATCH 4/5] iommu: introduce iommu_groups
Date: Fri, 31 May 2019 14:21:57 +0000	[thread overview]
Message-ID: <effeb9ace857427993a30f5575dc3a27@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <5CF1368C02000078002340B4@prv1-mh.provo.novell.com>

> -----Original Message-----
[snip]
> >> > --- a/xen/include/xen/pci.h
> >> > +++ b/xen/include/xen/pci.h
> >> > @@ -75,6 +75,9 @@ struct pci_dev {
> >> >      struct list_head alldevs_list;
> >> >      struct list_head domain_list;
> >> >
> >> > +    struct list_head grpdevs_list;
> >>
> >> Does this separate list provide much value? The devices in a group
> >> are going to move between two domain_list-s all in one go, so
> >> once you know the domain of one you'll be able to find the rest by
> >> iterating that domain's list. Is the fear that such an iteration may
> >> be tens of thousands of entries long, and hence become an issue
> >> when traversed? I have no idea how many PCI devices the biggest
> >> systems today would have, but if traversal was an issue, then it
> >> would already be with the code we've got now.
> >
> > I'd prefer to keep it... It makes the re-implementation of the domctl in the
> > next patch more straightforward.
> 
> I can accept this as the positive side. But there's extra storage
> needed (not much, but anyway), and the more (independent)
> lists we have that devices can be on, the more likely it'll be that
> one of them gets screwed up at some point (e.g. by forgetting
> to remove a device from one of them prior to de-allocation).

Ok, I'll drop the list and just match on the grp pointer.

  Paul

> 
> Jan
> 

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