Am 31.03.20 um 15:19 schrieb Chris Wilson:
Quoting Daniel Vetter (2020-03-31 11:38:50)
On Tue, Mar 31, 2020 at 11:20 AM Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
Quoting Daniel Vetter (2020-03-31 10:16:18)
On Tue, Mar 31, 2020 at 10:59:45AM +0200, Christian König wrote:
A not so gentle ping, since this pretty much broke all TTM based drivers.
Could we revert this for now?
Always ack for revert.
Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
So you didn't check the earlier patch either?
I did, but wasn't super sold on the idea of more flags to smack an r-b
onto it, so figured I'll throw the default ack-for-revert on this
meanwhile.
We allow userspace to poison the drm_mm at roughly 8K intervals, a
search space of 35b with typically O(N^2) behaviour and each node
traversal (rb_next/rb_prev) will itself be costly. Even our simple tests
can generate a search of several minutes before our patience runs out.o
Any drm_mm that allows for userspace to control alignment can be
arbitrarily fragmented, hence a raised eyebrow that this search would be
allowed in atomic context.
Wow, that is indeed quite a lot.
What is the criteria use for ordering the tree? Just the size or is that
size+alignment?
Never looked into this, but maybe we have a low hanging fruit for an
improvement here?
I'm not 100% sure, but moving away from atomic context wouldn't be that
easy.
Christian.
-Chris
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