Instead of attempting to recycle a request in to the cache when it retires, stuff a new one in the cache every time we allocate a request for some other reason.
Signed-off-by: Jason Ekstrand jason@jlekstrand.net Cc: Jon Bloomfield jon.bloomfield@intel.com Cc: Daniel Vetter daniel.vetter@intel.com Cc: Matthew Auld matthew.auld@intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com --- drivers/gpu/drm/i915/i915_request.c | 66 ++++++++++++++--------------- 1 file changed, 31 insertions(+), 35 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 48c5f8527854b..e531c74f0b0e2 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -128,41 +128,6 @@ static void i915_fence_release(struct dma_fence *fence) i915_sw_fence_fini(&rq->submit); i915_sw_fence_fini(&rq->semaphore);
- /* - * Keep one request on each engine for reserved use under mempressure - * - * We do not hold a reference to the engine here and so have to be - * very careful in what rq->engine we poke. The virtual engine is - * referenced via the rq->context and we released that ref during - * i915_request_retire(), ergo we must not dereference a virtual - * engine here. Not that we would want to, as the only consumer of - * the reserved engine->request_pool is the power management parking, - * which must-not-fail, and that is only run on the physical engines. - * - * Since the request must have been executed to be have completed, - * we know that it will have been processed by the HW and will - * not be unsubmitted again, so rq->engine and rq->execution_mask - * at this point is stable. rq->execution_mask will be a single - * bit if the last and _only_ engine it could execution on was a - * physical engine, if it's multiple bits then it started on and - * could still be on a virtual engine. Thus if the mask is not a - * power-of-two we assume that rq->engine may still be a virtual - * engine and so a dangling invalid pointer that we cannot dereference - * - * For example, consider the flow of a bonded request through a virtual - * engine. The request is created with a wide engine mask (all engines - * that we might execute on). On processing the bond, the request mask - * is reduced to one or more engines. If the request is subsequently - * bound to a single engine, it will then be constrained to only - * execute on that engine and never returned to the virtual engine - * after timeslicing away, see __unwind_incomplete_requests(). Thus we - * know that if the rq->execution_mask is a single bit, rq->engine - * can be a physical engine with the exact corresponding mask. - */ - if (is_power_of_2(rq->execution_mask) && - !cmpxchg(&rq->engine->request_pool, NULL, rq)) - return; - kmem_cache_free(global.slab_requests, rq); }
@@ -869,6 +834,29 @@ static void retire_requests(struct intel_timeline *tl) break; }
+static void +ensure_cached_request(struct i915_request **rsvd, gfp_t gfp) +{ + struct i915_request *rq; + + /* Don't try to add to the cache if we don't allow blocking. That + * just increases the chance that the actual allocation will fail. + */ + if (gfpflags_allow_blocking(gfp)) + return; + + if (READ_ONCE(rsvd)) + return; + + rq = kmem_cache_alloc(global.slab_requests, + gfp | __GFP_RETRY_MAYFAIL | __GFP_NOWARN); + if (!rq) + return; /* Oops but nothing we can do */ + + if (cmpxchg(rsvd, NULL, rq)) + kmem_cache_free(global.slab_requests, rq); +} + static noinline struct i915_request * request_alloc_slow(struct intel_timeline *tl, struct i915_request **rsvd, @@ -937,6 +925,14 @@ __i915_request_create(struct intel_context *ce, gfp_t gfp) /* Check that the caller provided an already pinned context */ __intel_context_pin(ce);
+ /* Before we do anything, try to make sure we have at least one + * request in the engine's cache. If we get here with GPF_NOWAIT + * (this can happen when switching to a kernel context), we we want + * to try very hard to not fail and we fall back to this cache. + * Top it off with a fresh request whenever it's empty. + */ + ensure_cached_request(&ce->engine->request_pool, gfp); + /* * Beware: Dragons be flying overhead. *