Add a tiny per-engine request mempool so that we should always have a
request available for powermanagement allocations from tricky
contexts. This reserve is expected to be only used for kernel
contexts when barriers must be emitted [almost] without fail.
The main consumer for this reserved request is expected to be engine-pm,
for which we know that there will always be at least the previous pm
request that we can reuse under mempressure (so there should always be
a spare request for engine_park()).
This is an alternative to using a comparatively bulky mempool, which
requires custom handling for both our reserved allocation requirement
and to protect our TYPESAFE_BY_RCU slab cache.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/gt/intel_engine_cs.c | 7 +++++
drivers/gpu/drm/i915/gt/intel_engine_types.h | 3 +++
drivers/gpu/drm/i915/i915_request.c | 27 ++++++++++++++++----
drivers/gpu/drm/i915/i915_request.h | 2 ++
4 files changed, 34 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 843cb6f2f696..5f45c8274203 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -431,7 +431,14 @@ void intel_engines_free(struct intel_gt *gt)
struct intel_engine_cs *engine;
enum intel_engine_id id;
+ /* Free the requests! dma-resv keeps fences around for an eternity */
+ rcu_barrier();
+
for_each_engine(engine, gt, id) {
+ if (engine->request_pool)
+ kmem_cache_free(i915_request_slab_cache(),
+ engine->request_pool);
+
kfree(engine);
gt->engine[id] = NULL;
}
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
index 80cdde712842..de8e6edcf999 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -308,6 +308,9 @@ struct intel_engine_cs {
struct list_head hold; /* ready requests, but on hold */
} active;
+ /* keep a request in reserve for a [pm] barrier under oom */
+ struct i915_request *request_pool;
+
struct llist_head barrier_tasks;
struct intel_context *kernel_context; /* pinned */
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 3388c5b610c5..22635bbabf06 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -101,6 +101,11 @@ static signed long i915_fence_wait(struct dma_fence *fence,
timeout);
}
+struct kmem_cache *i915_request_slab_cache(void)
+{
+ return global.slab_requests;
+}
+
static void i915_fence_release(struct dma_fence *fence)
{
struct i915_request *rq = to_request(fence);
@@ -115,6 +120,10 @@ 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 */
+ if (!cmpxchg(&rq->engine->request_pool, NULL, rq))
+ return;
+
kmem_cache_free(global.slab_requests, rq);
}
@@ -629,14 +638,22 @@ static void retire_requests(struct intel_timeline *tl)
}
static noinline struct i915_request *
-request_alloc_slow(struct intel_timeline *tl, gfp_t gfp)
+request_alloc_slow(struct intel_timeline *tl,
+ struct i915_request **rsvd,
+ gfp_t gfp)
{
struct i915_request *rq;
- if (list_empty(&tl->requests))
- goto out;
+ /* If we cannot wait, dip into our reserves */
+ if (!gfpflags_allow_blocking(gfp)) {
+ rq = xchg(rsvd, NULL);
+ if (!rq) /* Use the normal failure path for one final WARN */
+ goto out;
- if (!gfpflags_allow_blocking(gfp))
+ return rq;
+ }
+
+ if (list_empty(&tl->requests))
goto out;
/* Move our oldest request to the slab-cache (if not in use!) */
@@ -721,7 +738,7 @@ __i915_request_create(struct intel_context *ce, gfp_t gfp)
rq = kmem_cache_alloc(global.slab_requests,
gfp | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
if (unlikely(!rq)) {
- rq = request_alloc_slow(tl, gfp);
+ rq = request_alloc_slow(tl, &ce->engine->request_pool, gfp);
if (!rq) {
ret = -ENOMEM;
goto err_unreserve;
diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
index 3c552bfea67a..d8ce908e1346 100644
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -300,6 +300,8 @@ static inline bool dma_fence_is_i915(const struct dma_fence *fence)
return fence->ops == &i915_fence_ops;
}
+struct kmem_cache *i915_request_slab_cache(void);
+
struct i915_request * __must_check
__i915_request_create(struct intel_context *ce, gfp_t gfp);
struct i915_request * __must_check
--
2.20.1
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