Currently on execlists, we use a local hwsp for the kernel_context,
rather than the engine's HWSP, as this is the default for execlists.
However, seqno rollover requires allocating a new HWSP cachline, and may
require pinning a new HWSP page in the GTT. This operation requiring
pinning in the GGTT is not allowed within the kernel_context timeline,
as doing so may require re-entering the kernel_context in order to evict
from the GGTT. As we want to avoid requiring a new HWSP for the
kernel_context, we can use the permanently pinned engine's HWSP instead.
However to do so we must prevent the use of semaphores reading the
kernel_context's HWSP, as the use of semaphores do not support rollover
onto the same cacheline. Fortunately, the kernel_context is mostly
isolated, so unlikely to give benefit to semaphores.
Reported-by: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
---
drivers/gpu/drm/i915/gt/intel_lrc.c | 14 ++++++++++++--
drivers/gpu/drm/i915/gt/selftest_lrc.c | 12 +++++++++---
drivers/gpu/drm/i915/i915_request.c | 14 +++++++++-----
3 files changed, 30 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c
b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 70d91ad923ef..902d440ef07d 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -2964,7 +2964,8 @@ static int gen8_emit_init_breadcrumb(struct i915_request
*rq)
{
u32 *cs;
- GEM_BUG_ON(!i915_request_timeline(rq)->has_initial_breadcrumb);
+ if (!i915_request_timeline(rq)->has_initial_breadcrumb)
+ return 0;
cs = intel_ring_begin(rq, 6);
if (IS_ERR(cs))
@@ -4616,8 +4617,17 @@ static int __execlists_context_alloc(struct
intel_context *ce,
if (!ce->timeline) {
struct intel_timeline *tl;
+ struct i915_vma *hwsp;
+
+ /*
+ * Use the static global HWSP for the kernel context, and
+ * a dynamically allocated cacheline for everyone else.
+ */
+ hwsp = NULL;
+ if (unlikely(intel_context_is_barrier(ce)))
+ hwsp = engine->status_page.vma;
- tl = intel_timeline_create(engine->gt, NULL);
+ tl = intel_timeline_create(engine->gt, hwsp);
if (IS_ERR(tl)) {
ret = PTR_ERR(tl);
goto error_deref_obj;
diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c
b/drivers/gpu/drm/i915/gt/selftest_lrc.c
index ccd4cd2c202d..6f458f6d5523 100644
--- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
+++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
@@ -3494,15 +3494,21 @@ static int bond_virtual_engine(struct intel_gt *gt,
rq[0] = ERR_PTR(-ENOMEM);
for_each_engine(master, gt, id) {
struct i915_sw_fence fence = {};
+ struct intel_context *ce;
if (master->class == class)
continue;
+ ce = intel_context_create(master);
+ if (IS_ERR(ce)) {
+ err = PTR_ERR(ce);
+ goto out;
+ }
+
memset_p((void *)rq, ERR_PTR(-EINVAL), ARRAY_SIZE(rq));
- rq[0] = igt_spinner_create_request(&spin,
- master->kernel_context,
- MI_NOOP);
+ rq[0] = igt_spinner_create_request(&spin, ce, MI_NOOP);
+ intel_context_put(ce);
if (IS_ERR(rq[0])) {
err = PTR_ERR(rq[0]);
goto out;
diff --git a/drivers/gpu/drm/i915/i915_request.c
b/drivers/gpu/drm/i915/i915_request.c
index 0ecc2cf64216..1adb8cf35f75 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -886,6 +886,12 @@ emit_semaphore_wait(struct i915_request *to,
struct i915_request *from,
gfp_t gfp)
{
+ if (!intel_context_use_semaphores(to->context))
+ goto await_fence;
+
+ if (!rcu_access_pointer(from->hwsp_cacheline))
+ goto await_fence;
+
/* Just emit the first semaphore we see as request space is limited. */
if (already_busywaiting(to) & from->engine->mask)
goto await_fence;
@@ -931,12 +937,8 @@ i915_request_await_request(struct i915_request *to, struct
i915_request *from)
ret = i915_sw_fence_await_sw_fence_gfp(&to->submit,
&from->submit,
I915_FENCE_GFP);
- else if (intel_context_use_semaphores(to->context))
- ret = emit_semaphore_wait(to, from, I915_FENCE_GFP);
else
- ret = i915_sw_fence_await_dma_fence(&to->submit,
- &from->fence, 0,
- I915_FENCE_GFP);
+ ret = emit_semaphore_wait(to, from, I915_FENCE_GFP);
if (ret < 0)
return ret;
@@ -1035,6 +1037,8 @@ __i915_request_await_execution(struct i915_request *to,
{
int err;
+ GEM_BUG_ON(intel_context_is_barrier(from->context));
+
/* Submit both requests at the same time */
err = __await_execution(to, from, hook, I915_FENCE_GFP);
if (err)
--
2.25.0
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