On 17.01.2012, at 12:31, Paul Mackerras wrote:

On Tue, Jan 17, 2012 at 10:27:26AM +0100, Alexander Graf wrote:
=20

quoted

The thing I was getting at was not the map during the lifetime, but
the map during registration. Currently we have:
=20
1) Set VPA to x
2) Assign feature y to VPA
3) Use VPA
=20
1 and 2 are the slow path, 3 occurs more frequently. So we want 3 to
be fast. 1 and 2 don't matter that much wrt performance.
=20
You are currently mapping the VPA at /, which gets you into this
map/unmap mess trying to free the previous mapping. If you moved the
map to step 2 and only stored the GPA at step 1, all map+unmap
operations except for final unmaps would be in one spot, so you
wouldn't need to construct this big complex state machine.

=20
That might simplify things - I'll try it and see.  The worry with
doing the map/pin at 2 is that if anything goes wrong we no longer
have the opportunity to return an error for the H_REGISTER_VPA call,
so I'll have to at least do some checking in 1, leading to possibly
more code overall.

Well, then map and unmap it in step 1 and map it in step 2 again. We're =
in the slow path so performance isn't critical. Readability and =
maintainability however are :)


Alex