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<body><span class="vcard"><a class="email" href="mailto:chris@chris-wilson.co.uk" title="Chris Wilson <chris@chris-wilson.co.uk>"> <span class="fn">Chris Wilson</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [CI][SHARDS] igt@gem_exec_fence@basic-await-default - fail - Failed assertion: out[n] == 0"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108888">bug 108888</a>
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<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>REOPENED
</td>
<td>RESOLVED
</td>
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<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>FIXED
</td>
</tr></table>
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [CI][SHARDS] igt@gem_exec_fence@basic-await-default - fail - Failed assertion: out[n] == 0"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108888#c3">Comment # 3</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [CI][SHARDS] igt@gem_exec_fence@basic-await-default - fail - Failed assertion: out[n] == 0"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108888">bug 108888</a>
from <span class="vcard"><a class="email" href="mailto:chris@chris-wilson.co.uk" title="Chris Wilson <chris@chris-wilson.co.uk>"> <span class="fn">Chris Wilson</span></a>
</span></b>
<pre>Haswell is no longer the odd one out,
commit 6faf5916e6beb0dedb0fcbbafbaa152adeaea758
Author: Chris Wilson <<a href="mailto:chris@chris-wilson.co.uk">chris@chris-wilson.co.uk</a>>
Date: Fri Dec 28 14:07:35 2018 +0000
drm/i915: Remove HW semaphores for gen7 inter-engine synchronisation
The writing is on the wall for the existence of a single execution queue
along each engine, and as a consequence we will not be able to track
dependencies along the HW queue itself, i.e. we will not be able to use
HW semaphores on gen7 as they use a global set of registers (and unlike
gen8+ we can not effectively target memory to keep per-context seqno and
dependencies).
On the positive side, when we implement request reordering for gen7 we
also can not presume a simple execution queue and would also require
removing the current semaphore generation code. So this bring us another
step closer to request reordering for ringbuffer submission!
The negative side is that using interrupts to drive inter-engine
synchronisation is much slower (4us -> 15us to do a nop on each of the 3
engines on ivb). This is much better than it was at the time of introducing
the HW semaphores and equally important userspace weaned itself off
intermixing dependent BLT/RENDER operations (the prime culprit was glyph
rendering in UXA). So while we regress the microbenchmarks, it should not
impact the user.
References: <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [CI][SHARDS] igt@gem_exec_fence@basic-await-default - fail - Failed assertion: out[n] == 0"
href="show_bug.cgi?id=108888">https://bugs.freedesktop.org/show_bug.cgi?id=108888</a>
Signed-off-by: Chris Wilson <<a href="mailto:chris@chris-wilson.co.uk">chris@chris-wilson.co.uk</a>>
Reviewed-by: Mika Kuoppala <<a href="mailto:mika.kuoppala@linux.intel.com">mika.kuoppala@linux.intel.com</a>>
Link:
<a href="https://patchwork.freedesktop.org/patch/msgid/20181228140736.32606-2-chris@chris-wilson.co.uk">https://patchwork.freedesktop.org/patch/msgid/20181228140736.32606-2-chris@chris-wilson.co.uk</a></pre>
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