43acd6516c
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