[Intel-gfx] [PATCH 2/3] drm/i915/perf: Remove gtt_offset from stream->oa_buffer.head/.tail

Ashutosh Dixit
2023-09-09T01:16:32Z

There is no reason to add gtt_offset to the cached head/tail pointers
stream->oa_buffer.head and stream->oa_buffer.tail. This causes the code to
constantly add gtt_offset and subtract gtt_offset and is error
prone (e.g. see previous patch).

It is much simpler to maintain stream->oa_buffer.head and
stream->oa_buffer.tail without adding gtt_offset to them and just allow for
the gtt_offset when reading/writing from/to HW registers.

Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
---
drivers/gpu/drm/i915/i915_perf.c | 53 ++++++++------------------------
1 file changed, 13 insertions(+), 40 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index ec0fc2934045a..1347e4ec9dd5a 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -543,10 +543,9 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
{
u32 gtt_offset = i915_ggtt_offset(stream->oa_buffer.vma);
int report_size = stream->oa_buffer.format->size;
- u32 head, tail, read_tail;
+ u32 tail, hw_tail;
unsigned long flags;
bool pollin;
- u32 hw_tail;
u32 partial_report_size;

/* We have to consider the (unlikely) possibility that read() errors
@@ -556,6 +555,7 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
spin_lock_irqsave(&stream->oa_buffer.ptr_lock, flags);

hw_tail = stream->perf->ops.oa_hw_tail_read(stream);
+ hw_tail -= gtt_offset;

/* The tail pointer increases in 64 byte increments, not in report_size
* steps. Also the report size may not be a power of 2. Compute
@@ -565,16 +565,8 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
partial_report_size %= report_size;

/* Subtract partial amount off the tail */
- hw_tail -= gtt_offset;
hw_tail = OA_TAKEN(hw_tail, partial_report_size);

- /* NB: The head we observe here might effectively be a little
- * out of date. If a read() is in progress, the head could be
- * anywhere between this head and stream->oa_buffer.tail.
- */
- head = stream->oa_buffer.head - gtt_offset;
- read_tail = stream->oa_buffer.tail - gtt_offset;
-
tail = hw_tail;

/* Walk the stream backward until we find a report with report
@@ -588,7 +580,7 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
* memory in the order they were written to.
* If not : (╯°□°）╯︵ ┻━┻
*/
- while (OA_TAKEN(tail, read_tail) >= report_size) {
+ while (OA_TAKEN(tail, stream->oa_buffer.tail) >= report_size) {
void *report = stream->oa_buffer.vaddr + tail;

if (oa_report_id(stream, report) ||
@@ -602,9 +594,9 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
__ratelimit(&stream->perf->tail_pointer_race))
drm_notice(&stream->uncore->i915->drm,
"unlanded report(s) head=0x%x tail=0x%x hw_tail=0x%x\n",
- head, tail, hw_tail);
+ stream->oa_buffer.head, tail, hw_tail);

- stream->oa_buffer.tail = gtt_offset + tail;
+ stream->oa_buffer.tail = tail;

pollin = OA_TAKEN(stream->oa_buffer.tail,
stream->oa_buffer.head) >= report_size;
@@ -754,13 +746,6 @@ static int gen8_append_oa_reports(struct i915_perf_stream *stream,

spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags);

- /*
- * NB: oa_buffer.head/tail include the gtt_offset which we don't want
- * while indexing relative to oa_buf_base.
- */
- head -= gtt_offset;
- tail -= gtt_offset;
-
/*
* An out of bounds or misaligned head or tail pointer implies a driver
* bug since we validate + align the tail pointers we read from the
@@ -896,9 +881,8 @@ static int gen8_append_oa_reports(struct i915_perf_stream *stream,
* We removed the gtt_offset for the copy loop above, indexing
* relative to oa_buf_base so put back here...
*/
- head += gtt_offset;
intel_uncore_write(uncore, oaheadptr,
- head & GEN12_OAG_OAHEADPTR_MASK);
+ (head + gtt_offset) & GEN12_OAG_OAHEADPTR_MASK);
stream->oa_buffer.head = head;

spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags);
@@ -1043,12 +1027,6 @@ static int gen7_append_oa_reports(struct i915_perf_stream *stream,

spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags);

- /* NB: oa_buffer.head/tail include the gtt_offset which we don't want
- * while indexing relative to oa_buf_base.
- */
- head -= gtt_offset;
- tail -= gtt_offset;
-
/* An out of bounds or misaligned head or tail pointer implies a driver
* bug since we validate + align the tail pointers we read from the
* hardware and we are in full control of the head pointer which should
@@ -1111,13 +1089,8 @@ static int gen7_append_oa_reports(struct i915_perf_stream *stream,
if (start_offset != *offset) {
spin_lock_irqsave(&stream->oa_buffer.ptr_lock, flags);

- /* We removed the gtt_offset for the copy loop above, indexing
- * relative to oa_buf_base so put back here...
- */
- head += gtt_offset;
-
intel_uncore_write(uncore, GEN7_OASTATUS2,
- (head & GEN7_OASTATUS2_HEAD_MASK) |
+ ((head + gtt_offset) & GEN7_OASTATUS2_HEAD_MASK) |
GEN7_OASTATUS2_MEM_SELECT_GGTT);
stream->oa_buffer.head = head;

@@ -1705,7 +1678,7 @@ static void gen7_init_oa_buffer(struct i915_perf_stream *stream)
*/
intel_uncore_write(uncore, GEN7_OASTATUS2, /* head */
gtt_offset | GEN7_OASTATUS2_MEM_SELECT_GGTT);
- stream->oa_buffer.head = gtt_offset;
+ stream->oa_buffer.head = 0;

intel_uncore_write(uncore, GEN7_OABUFFER, gtt_offset);

@@ -1713,7 +1686,7 @@ static void gen7_init_oa_buffer(struct i915_perf_stream *stream)
gtt_offset | OABUFFER_SIZE_16M);

/* Mark that we need updated tail pointers to read from... */
- stream->oa_buffer.tail = gtt_offset;
+ stream->oa_buffer.tail = 0;

spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags);

@@ -1747,7 +1720,7 @@ static void gen8_init_oa_buffer(struct i915_perf_stream *stream)

intel_uncore_write(uncore, GEN8_OASTATUS, 0);
intel_uncore_write(uncore, GEN8_OAHEADPTR, gtt_offset);
- stream->oa_buffer.head = gtt_offset;
+ stream->oa_buffer.head = 0;

intel_uncore_write(uncore, GEN8_OABUFFER_UDW, 0);

@@ -1764,7 +1737,7 @@ static void gen8_init_oa_buffer(struct i915_perf_stream *stream)
intel_uncore_write(uncore, GEN8_OATAILPTR, gtt_offset & GEN8_OATAILPTR_MASK);

/* Mark that we need updated tail pointers to read from... */
- stream->oa_buffer.tail = gtt_offset;
+ stream->oa_buffer.tail = 0;

/*
* Reset state used to recognise context switches, affecting which
@@ -1801,7 +1774,7 @@ static void gen12_init_oa_buffer(struct i915_perf_stream *stream)
intel_uncore_write(uncore, __oa_regs(stream)->oa_status, 0);
intel_uncore_write(uncore, __oa_regs(stream)->oa_head_ptr,
gtt_offset & GEN12_OAG_OAHEADPTR_MASK);
- stream->oa_buffer.head = gtt_offset;
+ stream->oa_buffer.head = 0;

/*
* PRM says:
@@ -1817,7 +1790,7 @@ static void gen12_init_oa_buffer(struct i915_perf_stream *stream)
gtt_offset & GEN12_OAG_OATAILPTR_MASK);

/* Mark that we need updated tail pointers to read from... */
- stream->oa_buffer.tail = gtt_offset;
+ stream->oa_buffer.tail = 0;

/*
* Reset state used to recognise context switches, affecting which
--
2.41.0