[Bug 107788] [CI][DRMTIP] igt at gem_exec_await@wide-context - fail - __gem_context_create(fd, &ctx_id) == 0

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107788

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #3 from Chris Wilson <chris at chris-wilson.co.uk> ---
commit 288f1ced5e24abe3e768224f701a205c3a7e16f9 (HEAD -> drm-intel-next-queued,
drm-intel/drm-intel-next-queued)
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Tue Sep 4 16:31:17 2018 +0100

    drm/i915: Reduce context HW ID lifetime

    Future gen reduce the number of bits we will have available to
    differentiate between contexts, so reduce the lifetime of the ID
    assignment from that of the context to its current active cycle (i.e.
    only while it is pinned for use by the HW, will it have a constant ID).
    This means that instead of a max of 2k allocated contexts (worst case
    before fun with bit twiddling), we instead have a limit of 2k in flight
    contexts (minus a few that have been pinned by the kernel or by perf).

    To reduce the number of contexts id we require, we allocate a context id
    on first and mark it as pinned for as long as the GEM context itself is,
    that is we keep it pinned it while active on each engine. If we exhaust
    our context id space, then we try to reclaim an id from an idle context.
    In the extreme case where all context ids are pinned by active contexts,
    we force the system to idle in order to recover ids.

    We cannot reduce the scope of an HW-ID to an engine (allowing the same
    gem_context to have different ids on each engine) as in the future we
    will need to preassign an id before we know which engine the
    context is being executed on.

    v2: Improved commentary (Tvrtko) [I tried at least]

    References: https://bugs.freedesktop.org/show_bug.cgi?id=107788
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
    Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Cc: Mika Kuoppala <mika.kuoppala at intel.com>
    Cc: Michel Thierry <michel.thierry at intel.com>
    Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
    Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
    Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20180904153117.3907-1-chris@chris-wilson.co.uk

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