[Intel-gfx] [PATCH 28/36] drm/i915: Cancel non-persistent contexts on close

[Bloomfield, Jon]

> -----Original Message-----
> From: Chris Wilson <chris at chris-wilson.co.uk>
> Sent: Thursday, August 29, 2019 1:12 AM
> To: intel-gfx at lists.freedesktop.org
> Cc: Chris Wilson <chris at chris-wilson.co.uk>; Joonas Lahtinen
> <joonas.lahtinen at linux.intel.com>; Winiarski, Michal
> <michal.winiarski at intel.com>; Bloomfield, Jon <jon.bloomfield at intel.com>
> Subject: [PATCH 28/36] drm/i915: Cancel non-persistent contexts on close
> 
> Normally, we rely on our hangcheck to prevent persistent batches from
> hogging the GPU. However, if the user disables hangcheck, this mechanism
> breaks down. Despite our insistence that this is unsafe, the users are
> equally insistent that they want to use endless batches and will disable
> the hangcheck mechanism. We are looking at perhaps replacing hangcheck
> with a softer mechanism, that sends a pulse down the engine to check if
> it is well. We can use the same preemptive pulse to flush an active
> persistent context off the GPU upon context close, preventing resources
> being lost and unkillable requests remaining on the GPU after process
> termination. To avoid changing the ABI and accidentally breaking
> existing userspace, we make the persistence of a context explicit and
> enable it by default (matching current ABI). Userspace can opt out of
> persistent mode (forcing requests to be cancelled when the context is
> closed by process termination or explicitly) by a context parameter. To
> facilitate existing use-cases of disabling hangcheck, if the modparam is
> disabled (i915.enable_hangcheck=0), we disable persistence mode by
> default.  (Note, one of the outcomes for supporting endless mode will be
> the removal of hangchecking, at which point opting into persistent mode
> will be mandatory, or maybe the default perhaps controlled by cgroups.)
> 
> Testcase: igt/gem_ctx_persistence
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Michał Winiarski <michal.winiarski at intel.com>
> Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> ---
Reviewed-by: Jon Bloomfield <jon.bloomfield at intel.com>