From 12124bea5b82dc1e917304aed703c27292270051 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Sat, 12 Aug 2017 16:27:24 +0100 Subject: [PATCH] drm/i915: Suppress switch_mm emission between the same aliasing_ppgtt 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 Signed-off-by: Chris Wilson Cc: Martin Peres Reviewed-by: Joonas Lahtinen Link: https://patchwork.freedesktop.org/patch/msgid/20170812152724.6883-1-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_gem_context.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c index ed91ac8..86ac74a 100644 --- a/drivers/gpu/drm/i915/i915_gem_context.c +++ b/drivers/gpu/drm/i915/i915_gem_context.c @@ -741,19 +741,19 @@ static inline bool skip_rcs_switch(struct i915_hw_ppgtt *ppgtt, } 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; @@ -797,7 +797,7 @@ static int do_rcs_switch(struct drm_i915_gem_request *req) 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 @@ -894,7 +894,7 @@ int i915_switch_context(struct drm_i915_gem_request *req) 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); @@ -905,6 +905,7 @@ int i915_switch_context(struct drm_i915_gem_request *req) ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine); } + engine->legacy_active_context = to; return 0; } -- 2.7.4