| Message ID | 20200903133144.740-1-mika.kuoppala@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/i915: Unlock the shared hwsp_gtt object after pinning | expand |
Quoting Mika Kuoppala (2020-09-03 14:31:44) > From: Thomas Hellström <thomas.hellstrom@intel.com> > > The hwsp_gtt object is used for sub-allocation and could therefore > be shared by many contexts causing unnecessary contention during > concurrent context pinning. > However since we're currently locking it only for pinning, it remains > resident until we unpin it, and therefore it's safe to drop the > lock early, allowing for concurrent thread access. > > Signed-off-by: Thomas Hellström <thomas.hellstrom@intel.com> > --- > drivers/gpu/drm/i915/gt/intel_context.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c > index 61b05cd4c47a..65e956ba19e1 100644 > --- a/drivers/gpu/drm/i915/gt/intel_context.c > +++ b/drivers/gpu/drm/i915/gt/intel_context.c > @@ -271,6 +271,13 @@ int __intel_context_do_pin_ww(struct intel_context *ce, > i915_active_release(&ce->active); > err_ctx_unpin: > intel_context_post_unpin(ce); > + > + /* > + * Unlock the hwsp_ggtt object since it's shared. This is fine for now > + * since the lock has been used for pinning only, not fencing. > + */ > + i915_gem_ww_unlock_single(ce->timeline->hwsp_ggtt->obj); The timeline is not special here, the same rules for locking/unlock can equally be applied to all the global state. You may even go as far as putting a local acquire context here, which would then have avoided the cross driver pollution. Anyway, if it works for the timeline, there is no reason to keep the other globals locked. They are pinned and on completely different usage cycles to the user objects. [They can't be evicted without interacting with the HW to ensure the context has been flushed, so far there has been no way to do so without stalling for a freshly submitted request, hence we let them retire gracefully and kick the kernel timelines to flush completed contexts.] -Chris
On 9/3/20 4:01 PM, Chris Wilson wrote: > Quoting Mika Kuoppala (2020-09-03 14:31:44) >> From: Thomas Hellström <thomas.hellstrom@intel.com> >> >> The hwsp_gtt object is used for sub-allocation and could therefore >> be shared by many contexts causing unnecessary contention during >> concurrent context pinning. >> However since we're currently locking it only for pinning, it remains >> resident until we unpin it, and therefore it's safe to drop the >> lock early, allowing for concurrent thread access. >> >> Signed-off-by: Thomas Hellström <thomas.hellstrom@intel.com> >> --- >> drivers/gpu/drm/i915/gt/intel_context.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c >> index 61b05cd4c47a..65e956ba19e1 100644 >> --- a/drivers/gpu/drm/i915/gt/intel_context.c >> +++ b/drivers/gpu/drm/i915/gt/intel_context.c >> @@ -271,6 +271,13 @@ int __intel_context_do_pin_ww(struct intel_context *ce, >> i915_active_release(&ce->active); >> err_ctx_unpin: >> intel_context_post_unpin(ce); >> + >> + /* >> + * Unlock the hwsp_ggtt object since it's shared. This is fine for now >> + * since the lock has been used for pinning only, not fencing. >> + */ >> + i915_gem_ww_unlock_single(ce->timeline->hwsp_ggtt->obj); > The timeline is not special here, the same rules for locking/unlock can > equally be applied to all the global state. You may even go as far as > putting a local acquire context here, which would then have avoided the > cross driver pollution. > > Anyway, if it works for the timeline, there is no reason to keep the > other globals locked. They are pinned and on completely different usage > cycles to the user objects. Agreed. In principle everything we want to perma-pin we can unlock early, Keeping it under the same acquire context makes it possible to do this as part of a bigger ww transaction. Although initially this solution was discarded in favour of removing the suballocation to be able to ditch the perma-pinning in the future. But is this acceptable to address the pi-isolated issue until we have something more thought-through in place? Or is there somethin specific you want me to change for a R-B? Thanks, Thomas
diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c index 61b05cd4c47a..65e956ba19e1 100644 --- a/drivers/gpu/drm/i915/gt/intel_context.c +++ b/drivers/gpu/drm/i915/gt/intel_context.c @@ -271,6 +271,13 @@ int __intel_context_do_pin_ww(struct intel_context *ce, i915_active_release(&ce->active); err_ctx_unpin: intel_context_post_unpin(ce); + + /* + * Unlock the hwsp_ggtt object since it's shared. This is fine for now + * since the lock has been used for pinning only, not fencing. + */ + i915_gem_ww_unlock_single(ce->timeline->hwsp_ggtt->obj); + return err; }