On 01/05/2020 11:18, Chris Wilson wrote:
The ring is a precious resource: we anticipate to only use a few hundred
bytes for a request, and only try to reserve that before we start. If we
go beyond our guess in building the request, then instead of waiting at
the start of execbuf before we hold any locks or other resources, we
may trigger a wait inside a critical region. One example is in using gpu
relocations, where currently we emit a new MI_BB_START from the ring
every time we overflow a page of relocation entries. However, instead of
insert the command into the precious ring, we can chain the next page of
relocation entries as MI_BB_START from the end of the previous.
v2: Delay the emit_bb_start until after all the chained vma
synchronisation is complete. Since the buffer pool batches are idle, this
_should_ be a no-op, but one day we may some fancy async GPU bindings
for new vma!
Testcase: igt/gem_exec_reloc/basic-many-active
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
.../gpu/drm/i915/gem/i915_gem_execbuffer.c | 130 +++++++++++++++---
1 file changed, 111 insertions(+), 19 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 414859fa2673..293bf06b65b2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -271,6 +271,7 @@ struct i915_execbuffer {
struct i915_request *rq;
u32 *rq_cmd;
unsigned int rq_size;
+ struct i915_vma *rq_vma;
} reloc_cache;
u64 invalid_flags; /** Set of execobj.flags that are invalid */
@@ -975,20 +976,111 @@ static inline struct i915_ggtt *cache_to_ggtt(struct reloc_cache *cache)
return &i915->ggtt;
}
+static int reloc_gpu_chain(struct reloc_cache *cache)
+{
+ struct intel_gt_buffer_pool_node *pool;
+ struct i915_request *rq = cache->rq;
+ struct i915_vma *batch;
+ u32 *cmd;
+ int err;
+
+ pool = intel_gt_get_buffer_pool(rq->engine->gt, PAGE_SIZE);
+ if (IS_ERR(pool))
+ return PTR_ERR(pool);
+
+ batch = i915_vma_instance(pool->obj, rq->context->vm, NULL);
+ if (IS_ERR(batch)) {
+ err = PTR_ERR(batch);
+ goto out_pool;
+ }
+
+ err = i915_vma_pin(batch, 0, 0, PIN_USER | PIN_NONBLOCK);
+ if (err)
+ goto out_pool;
+
+ cmd = cache->rq_cmd + cache->rq_size;
+ *cmd++ = MI_ARB_CHECK;
+ if (cache->gen >= 8) {
+ *cmd++ = MI_BATCH_BUFFER_START_GEN8;
+ *cmd++ = lower_32_bits(batch->node.start);
+ *cmd++ = upper_32_bits(batch->node.start);
+ } else {
+ *cmd++ = MI_BATCH_BUFFER_START;
+ *cmd++ = lower_32_bits(batch->node.start);
+ }
+ i915_gem_object_flush_map(cache->rq_vma->obj);
+ i915_gem_object_unpin_map(cache->rq_vma->obj);
+ cache->rq_vma = NULL;
+
+ err = intel_gt_buffer_pool_mark_active(pool, rq);
+ if (err == 0) {
+ i915_vma_lock(batch);
+ err = i915_request_await_object(rq, batch->obj, false);
+ if (err == 0)
+ err = i915_vma_move_to_active(batch, rq, 0);
+ i915_vma_unlock(batch);
+ }
+ i915_vma_unpin(batch);
+ if (err)
+ goto out_pool;
+
+ cmd = i915_gem_object_pin_map(pool->obj,
batch->obj maybe to be consistent in this block? Few lines above you get
to it via batch.
+ cache->has_llc ?
+ I915_MAP_FORCE_WB :
+ I915_MAP_FORCE_WC);
+ if (IS_ERR(cmd)) {
+ err = PTR_ERR(cmd);
+ goto out_pool;
+ }
+
+ /* Return with batch mapping (cmd) still pinned */
+ cache->rq_cmd = cmd;
+ cache->rq_size = 0;
+ cache->rq_vma = batch;
+
+out_pool:
+ intel_gt_buffer_pool_put(pool);
+ return err;
+}
+
+static unsigned int reloc_bb_flags(const struct reloc_cache *cache)
+{
+ return cache->gen > 5 ? 0 : I915_DISPATCH_SECURE;
+}
+
static void reloc_gpu_flush(struct reloc_cache *cache)
{
- struct drm_i915_gem_object *obj = cache->rq->batch->obj;
+ struct i915_request *rq;
+ int err;
- GEM_BUG_ON(cache->rq_size >= obj->base.size / sizeof(u32));
- cache->rq_cmd[cache->rq_size] = MI_BATCH_BUFFER_END;
+ rq = fetch_and_zero(&cache->rq);
+ if (!rq)
+ return;
- __i915_gem_object_flush_map(obj, 0, sizeof(u32) * (cache->rq_size + 1));
- i915_gem_object_unpin_map(obj);
+ if (cache->rq_vma) {
+ struct drm_i915_gem_object *obj = cache->rq_vma->obj;
- intel_gt_chipset_flush(cache->rq->engine->gt);
+ GEM_BUG_ON(cache->rq_size >= obj->base.size / sizeof(u32));
+ cache->rq_cmd[cache->rq_size++] = MI_BATCH_BUFFER_END;
- i915_request_add(cache->rq);
- cache->rq = NULL;
+ __i915_gem_object_flush_map(obj,
+ 0, sizeof(u32) * cache->rq_size);
+ i915_gem_object_unpin_map(obj);
+ }
+
+ err = 0;
+ if (rq->engine->emit_init_breadcrumb)
+ err = rq->engine->emit_init_breadcrumb(rq);
+ if (!err)
+ err = rq->engine->emit_bb_start(rq,
+ rq->batch->node.start,
+ PAGE_SIZE,
+ reloc_bb_flags(cache));
+ if (err)
+ i915_request_set_error_once(rq, err);
Will this error propagate and fail the execbuf?
+
+ intel_gt_chipset_flush(rq->engine->gt);
+ i915_request_add(rq);
}
static void reloc_cache_reset(struct reloc_cache *cache)
@@ -1237,12 +1329,6 @@ static int __reloc_gpu_alloc(struct i915_execbuffer *eb,
if (err)
goto err_request;
- err = eb->engine->emit_bb_start(rq,
- batch->node.start, PAGE_SIZE,
- cache->gen > 5 ? 0 : I915_DISPATCH_SECURE);
- if (err)
- goto skip_request;
-
i915_vma_lock(batch);
err = i915_request_await_object(rq, batch->obj, false);
if (err == 0)
@@ -1257,6 +1343,7 @@ static int __reloc_gpu_alloc(struct i915_execbuffer *eb,
cache->rq = rq;
cache->rq_cmd = cmd;
cache->rq_size = 0;
+ cache->rq_vma = batch;
/* Return with batch mapping (cmd) still pinned */
goto out_pool;
@@ -1280,13 +1367,9 @@ static u32 *reloc_gpu(struct i915_execbuffer *eb,
{
struct reloc_cache *cache = &eb->reloc_cache;
u32 *cmd;
-
- if (cache->rq_size > PAGE_SIZE/sizeof(u32) - (len + 1))
- reloc_gpu_flush(cache);
+ int err;
if (unlikely(!cache->rq)) {
- int err;
-
if (!intel_engine_can_store_dword(eb->engine))
return ERR_PTR(-ENODEV);
@@ -1295,6 +1378,15 @@ static u32 *reloc_gpu(struct i915_execbuffer *eb,
return ERR_PTR(err);
}
+ if (unlikely(cache->rq_size + len > PAGE_SIZE / sizeof(u32) - 4)) {
4 dwords for the chain, ok.
+ err = reloc_gpu_chain(cache);
+ if (unlikely(err)) {
+ i915_request_set_error_once(cache->rq, err);
+ return ERR_PTR(err);
+ }
+ }
+
+ GEM_BUG_ON(cache->rq_size + len >= PAGE_SIZE / sizeof(u32));
cmd = cache->rq_cmd + cache->rq_size;
cache->rq_size += len;
Regards,
Tvrtko
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