From 430ffaf46c05bda56535893f38e684f5418c4c93 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Sat, 12 Aug 2017 16:27:24 +0100
Subject: [PATCH] drm/i915: Suppress switch_mm emission between the same aliasing_ppgtt
Git-commit: 430ffaf46c05bda56535893f38e684f5418c4c93
Patch-mainline: v4.13-rc6
References: FATE#322643 bsc#1055900
No-fix: 12124bea5b82dc1e917304aed703c27292270051
When switching between contexts using the aliasing_ppgtt, the VM is
shared. We don't need to reload the PD registers unless they are dirty.
Martin Peres reported an issue that looks like corruption between
Haswell context switches, bisecting to commit f9326be5f1d3 ("drm/i915:
Rearrange switch_context to load the aliasing ppgtt on first use").
Switching between the same mm (the aliasing_ppgtt is used for all
contexts in this case) should be a nop, but appears to trigger some
side-effects in the context switch. However, as we know the switch
is redundant in this case, we can skip it and continue to ignore the
issue until somebody feels strong enough to investigate full-ppgtt on
gen7 again!
Except.. Martin was using full-ppgtt which is not supported as it
doesn't work correctly yet. So whilst the bisect did yield valuable
information about the failures, the fix should not have any user impact
under default settings, with the exception of a slightly lower
throughput on xcs as the VM would always be reloaded.
V2: Also remember to set the legacy_active_context following the switch
on xcs (commit e8a9c58fcd9a ("drm/i915: Unify active context tracking
between legacy/execlists/guc"))
Fixes: f9326be5f1d3 ("drm/i915: Rearrange switch_context to load the aliasing ppgtt on first use")
Fixes: e8a9c58fcd9a ("drm/i915: Unify active context tracking between legacy/execlists/guc")
Reported-by: Martin Peres <martin.peres@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Martin Peres <martin.peres@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170812152724.6883-1-chris@chris-wilson.co.uk
(cherry picked from commit 12124bea5b82dc1e917304aed703c27292270051)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/gpu/drm/i915/i915_gem_context.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -688,19 +688,19 @@ static inline bool skip_rcs_switch(struc
}
static bool
-needs_pd_load_pre(struct i915_hw_ppgtt *ppgtt,
- struct intel_engine_cs *engine,
- struct i915_gem_context *to)
+needs_pd_load_pre(struct i915_hw_ppgtt *ppgtt, struct intel_engine_cs *engine)
{
+ struct i915_gem_context *from = engine->legacy_active_context;
+
if (!ppgtt)
return false;
/* Always load the ppgtt on first use */
- if (!engine->legacy_active_context)
+ if (!from)
return true;
/* Same context without new entries, skip */
- if (engine->legacy_active_context == to &&
+ if ((!from->ppgtt || from->ppgtt == ppgtt) &&
!(intel_engine_flag(engine) & ppgtt->pd_dirty_rings))
return false;
@@ -744,7 +744,7 @@ static int do_rcs_switch(struct drm_i915
if (skip_rcs_switch(ppgtt, engine, to))
return 0;
- if (needs_pd_load_pre(ppgtt, engine, to)) {
+ if (needs_pd_load_pre(ppgtt, engine)) {
/* Older GENs and non render rings still want the load first,
* "PP_DCLV followed by PP_DIR_BASE register through Load
* Register Immediate commands in Ring Buffer before submitting
@@ -841,7 +841,7 @@ int i915_switch_context(struct drm_i915_
struct i915_hw_ppgtt *ppgtt =
to->ppgtt ?: req->i915->mm.aliasing_ppgtt;
- if (needs_pd_load_pre(ppgtt, engine, to)) {
+ if (needs_pd_load_pre(ppgtt, engine)) {
int ret;
trace_switch_mm(engine, to);
@@ -852,6 +852,7 @@ int i915_switch_context(struct drm_i915_
ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);
}
+ engine->legacy_active_context = to;
return 0;
}