[Intel-xe] [PATCH v2 07/31] drm/xe: Only try to lock external BOs in VM bind

[Matthew Brost]

On Tue, May 09, 2023 at 02:29:23PM +0200, Thomas Hellström wrote:
> 
> On 5/8/23 23:34, Rodrigo Vivi wrote:
> > On Mon, May 08, 2023 at 01:08:10AM +0000, Matthew Brost wrote:
> > > On Fri, May 05, 2023 at 02:40:40PM -0400, Rodrigo Vivi wrote:
> > > > On Mon, May 01, 2023 at 05:17:03PM -0700, Matthew Brost wrote:
> > > > > Not needed and causes some issues with bulk LRU moves.
> > > > I'm confused with this explanation and the code below.
> > > > could you please provide a bit more wording here?
> > > > 
> > > We only need to try to lock a BO if it external as non-external BOs
> > > share the dma-resv with the already locked VM. Trying to lock
> > > non-external BOs caused an issue (list corruption) in an uncoming patch
> 
> s/uncoming/upcoming/
> 
> Also it's not clear to me how this could fix a list corruption in the bulk
> LRU moves? I mean, if it's a duplicate lock then it gets removed from the tv
> list and not touched again? Could you explain the mechanism of the fix?
> 

I had my head wrappeed around this at one point but now I forget as I
coded this one a while ago. This changes later series (drm_exec
locking), so IMO not that big of a deal merge this along with the
following patch without further explaination but if you think it is a
huge deal I can try to figure out what the issue is again or another
option is just stage the LRU patch after drm_exec.

Open to whatever but prefer to leave as is.

Matt

> Thanks,
> 
> Thomas
> 
> 
> > > which adds bulk LRU move. Since this code isn't needed, remove it.
> > it makes more sense now. with this in commit msg (but with Christopher fix)
> > 
> > 
> > Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > 
> > 
> > > ^^^ How about this.
> > > 
> > > > > Signed-off-by: Matthew Brost <mattthew.brost at intel.com>
> > > > > ---
> > > > >   drivers/gpu/drm/xe/xe_vm.c | 8 +++++---
> > > > >   1 file changed, 5 insertions(+), 3 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> > > > > index 272f0f7f24fe..6c427ff92c44 100644
> > > > > --- a/drivers/gpu/drm/xe/xe_vm.c
> > > > > +++ b/drivers/gpu/drm/xe/xe_vm.c
> > > > > @@ -2064,9 +2064,11 @@ static int vm_bind_ioctl(struct xe_vm *vm, struct xe_vma *vma,
> > > > >   		 */
> > > > >   		xe_bo_get(vbo);
> > > > > -		tv_bo.bo = &vbo->ttm;
> > > > > -		tv_bo.num_shared = 1;
> > > > > -		list_add(&tv_bo.head, &objs);
> > > > > +		if (!vbo->vm) {
> > > > > +			tv_bo.bo = &vbo->ttm;
> > > > > +			tv_bo.num_shared = 1;
> > > > > +			list_add(&tv_bo.head, &objs);
> > > > > +		}
> > > > >   	}
> > > > >   again:
> > > > > -- 
> > > > > 2.34.1
> > > > >