Re: [PATCH 3/5] iommu: Limit iommu_attach/detach_device to devices with their own group

Will Deacon
2015-02-02T16:45:55Z

On Fri, Jan 30, 2015 at 12:28:14PM +0000, Joerg Roedel wrote:
> On Wed, Jan 28, 2015 at 02:35:24PM +0000, Will Deacon wrote:
> > On Tue, Jan 27, 2015 at 12:08:57AM +0000, Joerg Roedel wrote:
> > > @@ -51,6 +51,7 @@ struct iommu_group {
> > > void (*iommu_data_release)(void *iommu_data);
> > > char *name;
> > > int id;
> > > + unsigned dev_cnt;
> >
> > Is this actually used on a fast path, or can we just inspect the list of
> > devices on the group instead?
>
> Not really a fast path, but we have to hold the group mutex while
> traversing the list, which could hurt performance somewhere else. Are
> these 4 bytes a problem?

No problem, it just seemed a bit redundant to have two ways of describing
the same thing and having the pain of keeping them in sync with each other.

Will