Re: [PATCH v2 4/5] drm/i915: Spin for struct_mutex inside shrinker

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On pe, 2017-06-09 at 12:03 +0100, Chris Wilson wrote:
> Having resolved whether or not we would deadlock upon a call to
> mutex_lock(&dev->struct_mutex), we can then spin for the contended
> struct_mutex if we are not the owner. We cannot afford to simply block
> and wait for the mutex, as the owner may itself be waiting for the
> allocator -- i.e. a cyclic deadlock. This should significantly improve
> the chance of running the shrinker for other processes whilst the GPU is
> busy.
> 
> A more balanced approach would be to optimistically spin whilst the
> mutex owner was on the cpu and there was an opportunity to acquire the
> mutex for ourselves quickly. However, that requires support from
> kernel/locking/ and a new mutex_spin_trylock() primitive.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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