gen3 does not fully flush MI stores to memory on MI_FLUSH, such that a
subsequent read from e.g. the sampler can bypass the store and read the
stale value from memory. This is a serious issue when we are using MI
stores to rewrite the batches for relocation, as it means that the batch
is reading from random user/kernel memory. While it is particularly
sensitive [and detectable] for relocations, reading stale data at any
time is a worry.
Having started with a small number of delaying stores and doubling until
no more incoherency was seen over a few hours (with and without
background memory pressure), 32 was the magic number.
Note that it definitely doesn't fix the issue, merely adds a long delay
between requests, sufficient to mostly hide the problem, enough to raise
the mtbf to several hours. This is merely a stop gap.
v2: Follow more closer with the gen5 w/a and include some
post-invalidate flushes as well.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2018
References: a889580c08 ("drm/i915: Flush GPU relocs harder for gen3")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200612123949.7093-1-chris@chris-wilson.co.uk
We infrequently use the direct i915 backpointer from the i915_request,
so do we really need to waste the space in the struct for it? 8 bytes
from the most frequently allocated struct vs an 3 bytes and pointer
chasing in using rq->engine->i915?
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200602220953.21178-1-chris@chris-wilson.co.uk
Pull the routines for writing CS packets out of intel_ring_submission
into their own files. These are low level operations for building CS
instructions, rather than the logic for filling the global ring buffer
with requests, and we will want to reuse them outside of this context.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200601072446.19548-2-chris@chris-wilson.co.uk
