drm/i915: Remove wait priority boosting

Upon waiting a request (when asked), we gave that request a small
priority boost, not enough for it to cause preemption, but enough for it
to be scheduled next before all equals. We also used that bit to give
new clients a small priority boost, similar to FQ_CODEL, such that we
favoured short interactive tasks ahead of long running streams.

However, this is causing lots of complications with timeslicing where we
both want to honour the boost and yet ignore it. Those complications
cause unexpected user behaviour (tasks not being timesliced and run
concurrently as epxected), and the easiest way to resolve that is to
remove the boost. Hopefully, we can find a compromise again if we need
to, but in theory timeslicing itself and future more advanced schedulers
should give us the interactivity boost we seek.

Testcase: igt/gem_exec_schedule/lateslice
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200507152338.7452-3-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 966523a8503f1820ee974c199fc5595b4b74727a..d54a4933cc0573b2bc86ed44a79bf461b1c77598 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -2597,15 +2597,6 @@ static void eb_request_add(struct i915_execbuffer *eb)
                 */
                if (!(rq->sched.flags & I915_SCHED_HAS_SEMAPHORE_CHAIN))
                        attr.priority |= I915_PRIORITY_NOSEMAPHORE;
-
-               /*
-                * Boost priorities to new clients (new request flows).
-                *
-                * Allow interactive/synchronous clients to jump ahead of
-                * the bulk clients. (FQ_CODEL)
-                */
-               if (list_empty(&rq->sched.signalers_list))
-                       attr.priority |= I915_PRIORITY_WAIT;
        } else {
                /* Serialise with context_close via the add_to_timeline */
                i915_request_set_error_once(rq, -ENOENT);

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index dd0fd4c4cf3220088e91044867112d16f398c96c..59c99e2f02573ea7fb7abb7ac78bee78f66ae8af 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -438,9 +438,7 @@ static int effective_prio(const struct i915_request *rq)
        if (__i915_request_has_started(rq))
                prio |= I915_PRIORITY_NOSEMAPHORE;
 
-       /* Restrict mere WAIT boosts from triggering preemption */
-       BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK); /* only internal */
-       return prio | __NO_PREEMPTION;
+       return prio;
 }
 
 static int queue_prio(const struct intel_engine_execlists *execlists)

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 aa6d56e25a10ae3fa6b3a5d26a16e0d45bd69917..94eb63f309cefb954fc3bfc103d88f618201fda8 100644 (file)
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -258,7 +258,7 @@ static void guc_submit(struct intel_engine_cs *engine,
 
 static inline int rq_prio(const struct i915_request *rq)
 {
-       return rq->sched.attr.priority | __NO_PREEMPTION;
+       return rq->sched.attr.priority;
 }
 
 static struct i915_request *schedule_in(struct i915_request *rq, int idx)

diff --git a/drivers/gpu/drm/i915/i915_priolist_types.h b/drivers/gpu/drm/i915/i915_priolist_types.h
index 732aad1488813b867aa92d6cde8b64ee04b971b5..e18723d8df86b61d3c48a4a03e5871e2db469c07 100644 (file)
--- a/drivers/gpu/drm/i915/i915_priolist_types.h
+++ b/drivers/gpu/drm/i915/i915_priolist_types.h
@@ -24,14 +24,13 @@ enum {
        I915_PRIORITY_DISPLAY,
 };
 
-#define I915_USER_PRIORITY_SHIFT 2
+#define I915_USER_PRIORITY_SHIFT 1
 #define I915_USER_PRIORITY(x) ((x) << I915_USER_PRIORITY_SHIFT)
 
 #define I915_PRIORITY_COUNT BIT(I915_USER_PRIORITY_SHIFT)
 #define I915_PRIORITY_MASK (I915_PRIORITY_COUNT - 1)
 
-#define I915_PRIORITY_WAIT             ((u8)BIT(0))
-#define I915_PRIORITY_NOSEMAPHORE      ((u8)BIT(1))
+#define I915_PRIORITY_NOSEMAPHORE      ((u8)BIT(0))
 
 /* Smallest priority value that cannot be bumped. */
 #define I915_PRIORITY_INVALID (INT_MIN | (u8)I915_PRIORITY_MASK)
@@ -47,8 +46,6 @@ enum {
 #define I915_PRIORITY_UNPREEMPTABLE INT_MAX
 #define I915_PRIORITY_BARRIER INT_MAX
 
-#define __NO_PREEMPTION (I915_PRIORITY_WAIT)
-
 struct i915_priolist {
        struct list_head requests[I915_PRIORITY_COUNT];
        struct rb_node node;

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 3c38d61c90f824c66e64ade3d34c08772828df20..589739bfee25af9d0a5d8825ca5d878cc77a8dec 100644 (file)
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1464,8 +1464,6 @@ void i915_request_add(struct i915_request *rq)
 
        if (!(rq->sched.flags & I915_SCHED_HAS_SEMAPHORE_CHAIN))
                attr.priority |= I915_PRIORITY_NOSEMAPHORE;
-       if (list_empty(&rq->sched.signalers_list))
-               attr.priority |= I915_PRIORITY_WAIT;
 
        __i915_request_queue(rq, &attr);
 
@@ -1651,7 +1649,6 @@ long i915_request_wait(struct i915_request *rq,
        if (flags & I915_WAIT_PRIORITY) {
                if (!i915_request_started(rq) && INTEL_GEN(rq->i915) >= 6)
                        intel_rps_boost(rq);
-               i915_schedule_bump_priority(rq, I915_PRIORITY_WAIT);
        }
 
        wait.tsk = current;

diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
index 6e2d4190099fb401df5a53885befe6a534d7bebe..bec2a9c254257f4dd6441997729d45918327e77b 100644 (file)
--- a/drivers/gpu/drm/i915/i915_scheduler.c
+++ b/drivers/gpu/drm/i915/i915_scheduler.c
@@ -174,7 +174,7 @@ sched_lock_engine(const struct i915_sched_node *node,
 
 static inline int rq_prio(const struct i915_request *rq)
 {
-       return rq->sched.attr.priority | __NO_PREEMPTION;
+       return rq->sched.attr.priority;
 }
 
 static inline bool need_preempt(int prio, int active)
@@ -443,16 +443,6 @@ bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
                list_add_rcu(&dep->signal_link, &node->signalers_list);
                list_add_rcu(&dep->wait_link, &signal->waiters_list);
 
-               /*
-                * As we do not allow WAIT to preempt inflight requests,
-                * once we have executed a request, along with triggering
-                * any execution callbacks, we must preserve its ordering
-                * within the non-preemptible FIFO.
-                */
-               BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK);
-               if (flags & I915_DEPENDENCY_EXTERNAL)
-                       __bump_priority(signal, __NO_PREEMPTION);
-
                ret = true;
        }