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

[Chris Wilson]

Quoting Bloomfield, Jon (2019-08-29 16:44:41)
> > -----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>

One thing I could do with for this is an ack from whomever is volunteered
to add the userspace support :)
-Chris