Re: [Intel-gfx] [PATCH 10/46] drm/i915/guc: Take engine PM when a context is pinned with GuC submission

Matthew Brost
2021-08-09T18:11:41Z

On Mon, Aug 09, 2021 at 04:23:42PM +0200, Daniel Vetter wrote:
> On Tue, Aug 03, 2021 at 03:29:07PM -0700, Matthew Brost wrote:
> > Taking a PM reference to prevent intel_gt_wait_for_idle from short
> > circuiting while a scheduling of user context could be enabled.
> >
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> > drivers/gpu/drm/i915/Makefile | 1 +
> > .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 36 +++++++++++++++++--
> > 2 files changed, 34 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> > index 903de270f2db..5e3a1e2095b0 100644
> > --- a/drivers/gpu/drm/i915/Makefile
> > +++ b/drivers/gpu/drm/i915/Makefile
> > @@ -103,6 +103,7 @@ gt-y += \
> > gt/intel_gt_clock_utils.o \
> > gt/intel_gt_irq.o \
> > gt/intel_gt_pm.o \
> > + gt/intel_gt_pm_unpark_work.o \
>
> This file isn't here?
>

Yep, included this in the wrong patch. Should be in:
https://patchwork.freedesktop.org/patch/448462/?series=92789&rev=2

> Also pm stuff tends to have very nasty locking requirements, doing special
> stuff like this in the backend tends to lead to really big surprises. I
> think two options to make sure our locking design stays consistent:
> - Lift this to generic code.

Not sure I'm following this, intel_engine_pm_get/put are generic calls.
Those calls should have all the correct annoations. If they don't we can
add them.

Matt

> - expose some engine_pm_migt_get/put() calls which do have the right set
> of might_lock annoations, and call those in the generic code.
>
> Imo the worst kernel abstractions are those where all implementations
> look&act the same, except for locking. Unfortunately i915-gem code is full
> of this stuff, and we need to stop this by enlisting lockdep to check the
> contracts for us.
> -Daniel
>
> > gt/intel_gt_pm_irq.o \
> > gt/intel_gt_requests.o \
> > gt/intel_gtt.o \
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > index 7fe4d1559a81..c5d9548bfd00 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -2056,7 +2056,12 @@ static int guc_context_pre_pin(struct intel_context *ce,
> >
> > static int guc_context_pin(struct intel_context *ce, void *vaddr)
> > {
> > - return __guc_context_pin(ce, ce->engine, vaddr);
> > + int ret = __guc_context_pin(ce, ce->engine, vaddr);
> > +
> > + if (likely(!ret && !intel_context_is_barrier(ce)))
> > + intel_engine_pm_get(ce->engine);
> > +
> > + return ret;
> > }
> >
> > static void guc_context_unpin(struct intel_context *ce)
> > @@ -2067,6 +2072,9 @@ static void guc_context_unpin(struct intel_context *ce)
> >
> > unpin_guc_id(guc, ce, true);
> > lrc_unpin(ce);
> > +
> > + if (likely(!intel_context_is_barrier(ce)))
> > + intel_engine_pm_put(ce->engine);
> > }
> >
> > static void guc_context_post_unpin(struct intel_context *ce)
> > @@ -3002,8 +3010,30 @@ static int guc_virtual_context_pre_pin(struct intel_context *ce,
> > static int guc_virtual_context_pin(struct intel_context *ce, void *vaddr)
> > {
> > struct intel_engine_cs *engine = guc_virtual_get_sibling(ce->engine, 0);
> > + int ret = __guc_context_pin(ce, engine, vaddr);
> > + intel_engine_mask_t tmp, mask = ce->engine->mask;
> > +
> > + if (likely(!ret))
> > + for_each_engine_masked(engine, ce->engine->gt, mask, tmp)
> > + intel_engine_pm_get(engine);
> >
> > - return __guc_context_pin(ce, engine, vaddr);
> > + return ret;
> > +}
> > +
> > +static void guc_virtual_context_unpin(struct intel_context *ce)
> > +{
> > + intel_engine_mask_t tmp, mask = ce->engine->mask;
> > + struct intel_engine_cs *engine;
> > + struct intel_guc *guc = ce_to_guc(ce);
> > +
> > + GEM_BUG_ON(context_enabled(ce));
> > + GEM_BUG_ON(intel_context_is_barrier(ce));
> > +
> > + unpin_guc_id(guc, ce, true);
> > + lrc_unpin(ce);
> > +
> > + for_each_engine_masked(engine, ce->engine->gt, mask, tmp)
> > + intel_engine_pm_put(engine);
> > }
> >
> > static void guc_virtual_context_enter(struct intel_context *ce)
> > @@ -3040,7 +3070,7 @@ static const struct intel_context_ops virtual_guc_context_ops = {
> >
> > .pre_pin = guc_virtual_context_pre_pin,
> > .pin = guc_virtual_context_pin,
> > - .unpin = guc_context_unpin,
> > + .unpin = guc_virtual_context_unpin,
> > .post_unpin = guc_context_post_unpin,
> >
> > .ban = guc_context_ban,
> > --
> > 2.28.0
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch