drm/i915: Cache last IRQ seqno to reduce IRQ overheadfence

The notify function can be called many times without the seqno
changing. Some are to prevent races due to the requirement of not
enabling interrupts until requested. However, when interrupts are
enabled the IRQ handler can be called multiple times without the
ring's seqno value changing. E.g. two interrupts are generated by
batch buffers completing in quick succession, the first call to the
handler processes both completions but the handler still gets executed
a second time. This patch reduces the overhead of these extra calls by
caching the last processed seqno value and early exiting if it has not
changed.

v3: New patch for series.

v5: Added comment about last_irq_seqno usage due to code review
feedback (Tvrtko Ursulin).

v6: Minor update to resolve a race condition with the wait_request
optimisation.

v7: Updated to newer nightly - lots of ring -> engine renaming plus an
interface change to get_seqno().

v10: Renamed the cached variable as it is no longer used at IRQ time.
[Review comment from Tvrtko Ursulin]

For: VIZ-5190
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

0 files changed, 0 insertions, 0 deletions