On 12/04/2014 10:17 AM, Chris Wilson wrote:
On Thu, Dec 04, 2014 at 10:02:19AM +0000, Tvrtko Ursulin wrote:
On 12/04/2014 09:48 AM, Chris Wilson wrote:
On Wed, Dec 03, 2014 at 02:59:24PM +0000, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Multiple GGTT VMAs per object will be introduced in the near future which will
make it impossible to guarantee normal GGTT view is at the head of the list.
Purpose of this patch is to break this assumption straight away so any
potential hidden assumptions in the code base can be bisected to this
simple patch.
No, please don't. The rationale for putting ggtt first is because it
puts the one vma that every object is likely to use at the front, and
makes it also the first in the list for debugging.
This came from talking with Daniel, but I don't understand why every
object is likely to have a GGTT mapping?
Because the userspace usage pattern is such that it is typical that
every object is accessed through the GTT at some point in its life.
It's actually becoming less so as we use alternative mmappings, but it
will remain so for quite some time yet.
With multiple GGTT views it may happen that only single GGTT VMA
exists in the list but it is not the one current code would expect.
So the idea was to break that to flesh out any potential hidden
assumptions in the code. (I did not find any by just looking
though.)
What kind of debugging you have in mind, error capture? Or actually
inspecting memory of a live kernel?
Error capture inspection of memory of a live kernel.
So personally you don't think it should be of any concern if a GGTT VMA
is at the head of the list, but it is not the same GGTT VMA which you
would find there in majority of cases?
Regards,
Tvrtko
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