[Intel-xe] [PATCH 1/3] drm/xe: Disable interruptable wait on xe_bo_move()

[Souza, Jose]

On Mon, 2023-05-29 at 16:46 +0200, Thomas Hellström wrote:
> On 5/29/23 16:40, Souza, Jose wrote:
> > On Mon, 2023-05-29 at 12:31 +0200, Thomas Hellström wrote:
> > > On Mon, 2023-05-29 at 10:59 +0200, Thomas Hellström wrote:
> > > > On Fri, 2023-05-26 at 12:06 -0700, José Roberto de Souza wrote:
> > > > > All the Xe users of dma_resv_wait_timeout() also disable the
> > > > > interruptable wait.
> > > > > And doing so this avoids DRM_IOCTL_XE_EXEC fails when under memory
> > > > > pressure.
> > > > Interruptible waits are crucial for signal delivery latency and for
> > > > user experience (being able to ctrl-c away from somtething that is
> > > > stuck).
> > > > 
> > > > Uninterruptible waits should only ever be used in situations where
> > > > it's
> > > > impossible to recover from an error, like in error or possibly
> > > > destruction paths.
> > > > 
> > > > In this case execbuf should be able to handle the -EINTR returned
> > > > from
> > > > the ioctl and restart. If it doesn't there's an error elsewhere.
> > > > 
> > > > But Maarten had a patch to return the real error code rather than
> > > > rewriting it to -ETIME.
> > This patch? https://patchwork.freedesktop.org/patch/539633/?series=118428&rev=1
> > 
> > This would cause it to return ERESTARTSYS to user-space.
> 
> ERESTARTSYS is a special error code that is never forwarded to 
> user-space, the kernel's signal handling functionality converts it to 
> EINTR iff there is a signal pending, and if not, just restarts the 
> system call internally without returning to user-space. So user-space 
> should just see the EINTR.

Okay. Tested and it indeed don't return ERESTARTSYS to user-space.

thanks for the clarification.

> 
> /Thomas
> 
> 
> > 
> > > > /Thomas
> > > Upon closer inspection of the code, that bool now set to true should
> > > really be ctx->interruptible. Still Maarten's patch would be needed to
> > > avoid the -ETIME rewrite, though.
> > > 
> > > /Thomas
> > > 
> > > 
> > > > 
> > > > 
> > > > > Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/239
> > > > > Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> > > > > Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > > > > Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> > > > > ---
> > > > >   drivers/gpu/drm/xe/xe_bo.c | 2 +-
> > > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/xe/xe_bo.c
> > > > > b/drivers/gpu/drm/xe/xe_bo.c
> > > > > index 0db9c05097d07..6ed7e08269e82 100644
> > > > > --- a/drivers/gpu/drm/xe/xe_bo.c
> > > > > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > > > > @@ -609,7 +609,7 @@ static int xe_bo_move(struct ttm_buffer_object
> > > > > *ttm_bo, bool evict,
> > > > >              new_mem->mem_type == XE_PL_SYSTEM) {
> > > > >                  long timeout = dma_resv_wait_timeout(ttm_bo-
> > > > > > base.resv,
> > > > >                                                      
> > > > > DMA_RESV_USAGE_BOOKKEEP,
> > > > > -                                                    true,
> > > > > +                                                    false,
> > > > >                                                      
> > > > > MAX_SCHEDULE_TIMEOUT);
> > > > >                  if (timeout <= 0) {
> > > > >                          ret = -ETIME;