Am 18.05.21 um 18:07 schrieb Thomas Hellström:
On 5/18/21 5:42 PM, Christian König wrote:
Am 18.05.21 um 17:38 schrieb Thomas Hellström:
On 5/18/21 5:28 PM, Christian König wrote:
Am 18.05.21 um 17:20 schrieb Thomas Hellström:
On 5/18/21 5:18 PM, Christian König wrote:
Am 18.05.21 um 17:15 schrieb Thomas Hellström: > > On 5/18/21 10:26 AM, Thomas Hellström wrote: >> We are calling the eviction_valuable driver callback at >> eviction time to >> determine whether we actually can evict a buffer object. >> The upcoming i915 TTM backend needs the same functionality for >> swapout, >> and that might actually be beneficial to other drivers as well. >> >> Add an eviction_valuable call also in the swapout path. Try to >> keep the >> current behaviour for all drivers by returning true if the >> buffer object >> is already in the TTM_PL_SYSTEM placement. We change behaviour >> for the >> case where a buffer object is in a TT backed placement when >> swapped out, >> in which case the drivers normal eviction_valuable path is run. >> >> Finally export ttm_tt_unpopulate() and don't swap out bos >> that are not populated. This allows a driver to purge a bo at >> swapout time if its content is no longer valuable rather than to >> have TTM swap the contents out. >> >> Cc: Christian König christian.koenig@amd.com >> Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com > > Christian, > > Here we have a ttm_tt_unpopulate() export as well at the end. I > figure you will push back on that one. What we really need is a > functionality to just drop the bo contents and end up in system > memory unpopulated. Should I perhaps add a utility function to > do that instead? like ttm_bo_purge()?
We already have that. Just call ttm_bo_validate() without any place to put the buffer.
See how ttm_bo_pipeline_gutting() is used.
Christian.
OK, so is that reentrant from the move() or swap_notify() callback.
That sounds like a design bug to me since you should never need to do this.
When you want to destroy the backing store of a buffer during eviction you should just do this by returning an empty placement from the evict_flags callback.
So this is for the functionality where the user has indicated that the contents is no longer of value, but the buffer itself is cached until evicted or swapped out for performance reasons. So the above would work for eviction, but what about swapout. Could we add some similar functionality there?
Amdgpu has the same functionality and you don't need to handle swap at all.
Just return from the evict_flags that you want to drop the backing store as soon as the BO leaves the GTT domain.
Hmm, the pipeline_gutting function seems ok, but overly complex if the bo is already idle, Am I allowed to optimize it slightly for the latter case?
Yeah, sure. We just never hat that use case so far.
Christian.
/Thomas
Christian.
/Thomas
Regards, Christian.
/Thomas
> > Thanks, > > Thomas > >