Commit 43acd651 authored by Chris Wilson's avatar Chris Wilson

drm/i915: Keep a per-engine request pool

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. The advantage of mempool
would be that it would allow us to keep a larger per-engine request
pool. However, converting over to mempool is straightforward should the
need arise.
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-and-tested-by: default avatarJanusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200402184037.21630-1-chris@chris-wilson.co.uk
parent 63d0f3ea
......@@ -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;
}
......
......@@ -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 */
......
......@@ -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))
/* 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;
......
......@@ -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
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment