[Intel-gfx] [PATCH 13/13] drm/i915: Cache last IRQ seqno to reduce IRQ overhead

Chris Wilson chris at chris-wilson.co.uk
Fri Dec 11 06:55:53 PST 2015

On Fri, Dec 11, 2015 at 01:12:01PM +0000, John.C.Harrison at Intel.com wrote:
> From: John Harrison <John.C.Harrison at Intel.com>
> The notify function can be called many times without the seqno
> changing. A large number of duplicates are to prevent races due to the
> requirement of not enabling interrupts until requested. However, when
> interrupts are enabled the IRQ handle can be called multiple times
> without the ring's seqno value changing. This patch reduces the
> overhead of these extra calls by caching the last processed seqno
> value and early exiting if it has not changed.

This is just plain wrong. Every user-interrupt is preceded by a seqno

Chris Wilson, Intel Open Source Technology Centre

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