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drm/i915: Keep a per-engine request pool

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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: Chris 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: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200402184037.21630-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson
2020-04-02 19:40:37 +01:00
parent 63d0f3ea8e
commit 43acd6516c
4 changed files with 34 additions and 5 deletions
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7
drivers/gpu/drm/i915/gt/intel_engine_cs.c
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@@ -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;
}