drm/i915: Micro-optimise hotpath through intel_ring_begin()

Typically, there is space available within the ring and if not we have
to wait (by definition a slow path). Rearrange the code to reduce the
number of branches and stack size for the hotpath, accomodating a slight
growth for the wait.

v2: Fix the new assert that packets are not larger than the actual ring.
v3: Make the parameters unsigned as well to make usage.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170504130846.4807-3-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2017-05-04 14:08:46 +01:00
Родитель 95aebcb2da
Коммит 5e5655c32d
2 изменённых файлов: 38 добавлений и 32 удалений

Просмотреть файл

@ -1656,7 +1656,8 @@ static int ring_request_alloc(struct drm_i915_gem_request *request)
return 0;
}
static int wait_for_space(struct drm_i915_gem_request *req, int bytes)
static noinline int wait_for_space(struct drm_i915_gem_request *req,
unsigned int bytes)
{
struct intel_ring *ring = req->ring;
struct drm_i915_gem_request *target;
@ -1701,52 +1702,56 @@ static int wait_for_space(struct drm_i915_gem_request *req, int bytes)
return 0;
}
u32 *intel_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
u32 *intel_ring_begin(struct drm_i915_gem_request *req,
unsigned int num_dwords)
{
struct intel_ring *ring = req->ring;
int remain_actual = ring->size - ring->emit;
int remain_usable = ring->effective_size - ring->emit;
int bytes = num_dwords * sizeof(u32);
int total_bytes, wait_bytes;
bool need_wrap = false;
const unsigned int remain_usable = ring->effective_size - ring->emit;
const unsigned int bytes = num_dwords * sizeof(u32);
unsigned int need_wrap = 0;
unsigned int total_bytes;
u32 *cs;
total_bytes = bytes + req->reserved_space;
GEM_BUG_ON(total_bytes > ring->effective_size);
if (unlikely(bytes > remain_usable)) {
/*
* Not enough space for the basic request. So need to flush
* out the remainder and then wait for base + reserved.
*/
wait_bytes = remain_actual + total_bytes;
need_wrap = true;
} else if (unlikely(total_bytes > remain_usable)) {
/*
* The base request will fit but the reserved space
* falls off the end. So we don't need an immediate wrap
* and only need to effectively wait for the reserved
* size space from the start of ringbuffer.
*/
wait_bytes = remain_actual + req->reserved_space;
} else {
/* No wrapping required, just waiting. */
wait_bytes = total_bytes;
if (unlikely(total_bytes > remain_usable)) {
const int remain_actual = ring->size - ring->emit;
if (bytes > remain_usable) {
/*
* Not enough space for the basic request. So need to
* flush out the remainder and then wait for
* base + reserved.
*/
total_bytes += remain_actual;
need_wrap = remain_actual | 1;
} else {
/*
* The base request will fit but the reserved space
* falls off the end. So we don't need an immediate
* wrap and only need to effectively wait for the
* reserved size from the start of ringbuffer.
*/
total_bytes = req->reserved_space + remain_actual;
}
}
if (wait_bytes > ring->space) {
int ret = wait_for_space(req, wait_bytes);
if (unlikely(total_bytes > ring->space)) {
int ret = wait_for_space(req, total_bytes);
if (unlikely(ret))
return ERR_PTR(ret);
}
if (unlikely(need_wrap)) {
GEM_BUG_ON(remain_actual > ring->space);
GEM_BUG_ON(ring->emit + remain_actual > ring->size);
need_wrap &= ~1;
GEM_BUG_ON(need_wrap > ring->space);
GEM_BUG_ON(ring->emit + need_wrap > ring->size);
/* Fill the tail with MI_NOOP */
memset(ring->vaddr + ring->emit, 0, remain_actual);
memset(ring->vaddr + ring->emit, 0, need_wrap);
ring->emit = 0;
ring->space -= remain_actual;
ring->space -= need_wrap;
}
GEM_BUG_ON(ring->emit > ring->size - bytes);

Просмотреть файл

@ -497,7 +497,8 @@ void intel_legacy_submission_resume(struct drm_i915_private *dev_priv);
int __must_check intel_ring_cacheline_align(struct drm_i915_gem_request *req);
u32 __must_check *intel_ring_begin(struct drm_i915_gem_request *req, int n);
u32 __must_check *intel_ring_begin(struct drm_i915_gem_request *req,
unsigned int n);
static inline void
intel_ring_advance(struct drm_i915_gem_request *req, u32 *cs)