Re: [RFC PATCH V3 06/17] ppc/pnv: allocate pe->iommu_table dynamically

On Wed, Jun 25, 2014 at 09:20:11AM +0000, David Laight wrote:

From: Wei Yang

quoted

On Wed, Jun 25, 2014 at 02:12:34PM +1000, Alexey Kardashevskiy wrote:

quoted

On 06/25/2014 11:12 AM, Wei Yang wrote:

quoted

On Tue, Jun 24, 2014 at 08:06:32PM +1000, Alexey Kardashevskiy wrote:

quoted

On 06/10/2014 11:56 AM, Wei Yang wrote:

quoted

Current iommu_table of a PE is a static field. This will have a problem when
iommu_free_table is called.

What kind of problem? This table is per PE and PE is not going anywhere.

Yes, for Bus PE, they will always sit in the system. When VF PE introduced,
they could be released on the fly. When they are released, so do the iommu
table for the PE.

iommu_table is a part of PE struct. When PE is released, iommu_table will
go with it as well. Why to make is a pointer? I would understand it if you
added reference counting there but no - iommu_table's lifetime is equal to
PE lifetime.

Yes, iommu_talbe's life time equals to PE lifetime, so when releasing a PE we
need to release the iommu table. Currently, there is one function to release
the iommu table, iommu_free_table() which takes a pointer of the iommu_table
and release it.

If the iommu table in PE is just a part of PE, it will have some problem to
release it with iommu_free_table(). That's why I make it a pointer in PE
structure.

What are the sizes of the iommu table and the PE structure?

I calculated it in my mind, the size of iommu_table, defined in
arch/powerpc/include/asm/iommu.h is 256 bytes.

If the table is a round number of pages then you probably don't want to
embed it inside the PE structure.

If my understanding is correct, the iommu table structure size is not that
big.

David

-- 
Richard Yang
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