Re: [Intel-gfx] [PATCH 41/46] drm/i915: Eliminate unnecessary VMA calls for multi-BB submission

Daniel Vetter
2021-08-09T17:07:50Z

On Tue, Aug 03, 2021 at 03:29:38PM -0700, Matthew Brost wrote:
> Certain VMA functions in the execbuf IOCTL only need to be called on
> first or last BB of a multi-BB submission. eb_relocate() on the first

eb_relocate should be outright disallowed on multi lrc execbuf ioctl.
There's no users of that left, and it does substantially simplify the
entire locking problem if we outright disallow that.

> and eb_release_vmas() on the last. Doing so will save CPU / GPU cycles.

Yah for our mix of pin/unpin vs dma_resv_lock/unlock. Now with the current
unpin design this move is ok, but we want/need to switch vma over to
dma_resv_lock. And then it gets really nasty, because you run into a ton
of problems.

To more I read this the less I like this :-/
-Daniel

>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
> .../gpu/drm/i915/gem/i915_gem_execbuffer.c | 127 +++++++++++-------
> .../i915/gem/selftests/i915_gem_execbuffer.c | 14 +-
> 2 files changed, 83 insertions(+), 58 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index ecdb583cc2eb..70784779872a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -270,7 +270,7 @@ struct i915_execbuffer {
> /** list of vma that have execobj.relocation_count */
> struct list_head relocs;
>
> - struct i915_gem_ww_ctx ww;
> + struct i915_gem_ww_ctx *ww;
>
> /**
> * Track the most recently used object for relocations, as we
> @@ -448,7 +448,7 @@ eb_pin_vma(struct i915_execbuffer *eb,
> pin_flags |= PIN_GLOBAL;
>
> /* Attempt to reuse the current location if available */
> - err = i915_vma_pin_ww(vma, &eb->ww, 0, 0, pin_flags);
> + err = i915_vma_pin_ww(vma, eb->ww, 0, 0, pin_flags);
> if (err == -EDEADLK)
> return err;
>
> @@ -457,11 +457,11 @@ eb_pin_vma(struct i915_execbuffer *eb,
> return err;
>
> /* Failing that pick any _free_ space if suitable */
> - err = i915_vma_pin_ww(vma, &eb->ww,
> - entry->pad_to_size,
> - entry->alignment,
> - eb_pin_flags(entry, ev->flags) |
> - PIN_USER | PIN_NOEVICT);
> + err = i915_vma_pin_ww(vma, eb->ww,
> + entry->pad_to_size,
> + entry->alignment,
> + eb_pin_flags(entry, ev->flags) |
> + PIN_USER | PIN_NOEVICT);
> if (unlikely(err))
> return err;
> }
> @@ -643,9 +643,9 @@ static int eb_reserve_vma(struct i915_execbuffer *eb,
> return err;
> }
>
> - err = i915_vma_pin_ww(vma, &eb->ww,
> - entry->pad_to_size, entry->alignment,
> - eb_pin_flags(entry, ev->flags) | pin_flags);
> + err = i915_vma_pin_ww(vma, eb->ww,
> + entry->pad_to_size, entry->alignment,
> + eb_pin_flags(entry, ev->flags) | pin_flags);
> if (err)
> return err;
>
> @@ -940,7 +940,7 @@ static int eb_lock_vmas(struct i915_execbuffer *eb)
> struct eb_vma *ev = &eb->vma[i];
> struct i915_vma *vma = ev->vma;
>
> - err = i915_gem_object_lock(vma->obj, &eb->ww);
> + err = i915_gem_object_lock(vma->obj, eb->ww);
> if (err)
> return err;
> }
> @@ -1020,12 +1020,13 @@ eb_get_vma(const struct i915_execbuffer *eb, unsigned long handle)
> }
> }
>
> -static void eb_release_vmas(struct i915_execbuffer *eb, bool final)
> +static void eb_release_vmas(struct i915_execbuffer *eb, bool final,
> + bool unreserve)
> {
> const unsigned int count = eb->buffer_count;
> unsigned int i;
>
> - for (i = 0; i < count; i++) {
> + for (i = 0; unreserve && i < count; i++) {
> struct eb_vma *ev = &eb->vma[i];
> struct i915_vma *vma = ev->vma;
>
> @@ -1237,7 +1238,7 @@ static void *reloc_iomap(struct drm_i915_gem_object *obj,
> if (err)
> return ERR_PTR(err);
>
> - vma = i915_gem_object_ggtt_pin_ww(obj, &eb->ww, NULL, 0, 0,
> + vma = i915_gem_object_ggtt_pin_ww(obj, eb->ww, NULL, 0, 0,
> PIN_MAPPABLE |
> PIN_NONBLOCK /* NOWARN */ |
> PIN_NOEVICT);
> @@ -1361,7 +1362,7 @@ static int __reloc_gpu_alloc(struct i915_execbuffer *eb,
> }
> eb->reloc_pool = NULL;
>
> - err = i915_gem_object_lock(pool->obj, &eb->ww);
> + err = i915_gem_object_lock(pool->obj, eb->ww);
> if (err)
> goto err_pool;
>
> @@ -1380,7 +1381,7 @@ static int __reloc_gpu_alloc(struct i915_execbuffer *eb,
> goto err_unmap;
> }
>
> - err = i915_vma_pin_ww(batch, &eb->ww, 0, 0, PIN_USER | PIN_NONBLOCK);
> + err = i915_vma_pin_ww(batch, eb->ww, 0, 0, PIN_USER | PIN_NONBLOCK);
> if (err)
> goto err_unmap;
>
> @@ -1402,7 +1403,7 @@ static int __reloc_gpu_alloc(struct i915_execbuffer *eb,
> eb->reloc_context = ce;
> }
>
> - err = intel_context_pin_ww(ce, &eb->ww);
> + err = intel_context_pin_ww(ce, eb->ww);
> if (err)
> goto err_unpin;
>
> @@ -2017,8 +2018,8 @@ static noinline int eb_relocate_parse_slow(struct i915_execbuffer *eb,
> }
>
> /* We may process another execbuffer during the unlock... */
> - eb_release_vmas(eb, false);
> - i915_gem_ww_ctx_fini(&eb->ww);
> + eb_release_vmas(eb, false, true);
> + i915_gem_ww_ctx_fini(eb->ww);
>
> if (rq) {
> /* nonblocking is always false */
> @@ -2062,7 +2063,7 @@ static noinline int eb_relocate_parse_slow(struct i915_execbuffer *eb,
> err = eb_reinit_userptr(eb);
>
> err_relock:
> - i915_gem_ww_ctx_init(&eb->ww, true);
> + i915_gem_ww_ctx_init(eb->ww, true);
> if (err)
> goto out;
>
> @@ -2119,8 +2120,8 @@ static noinline int eb_relocate_parse_slow(struct i915_execbuffer *eb,
>
> err:
> if (err == -EDEADLK) {
> - eb_release_vmas(eb, false);
> - err = i915_gem_ww_ctx_backoff(&eb->ww);
> + eb_release_vmas(eb, false, true);
> + err = i915_gem_ww_ctx_backoff(eb->ww);
> if (!err)
> goto repeat_validate;
> }
> @@ -2152,7 +2153,7 @@ static noinline int eb_relocate_parse_slow(struct i915_execbuffer *eb,
> return err;
> }
>
> -static int eb_relocate_parse(struct i915_execbuffer *eb)
> +static int eb_relocate_parse(struct i915_execbuffer *eb, bool first)
> {
> int err;
> struct i915_request *rq = NULL;
> @@ -2189,14 +2190,16 @@ static int eb_relocate_parse(struct i915_execbuffer *eb)
> /* only throttle once, even if we didn't need to throttle */
> throttle = false;
>
> - err = eb_validate_vmas(eb);
> - if (err == -EAGAIN)
> - goto slow;
> - else if (err)
> - goto err;
> + if (first) {
> + err = eb_validate_vmas(eb);
> + if (err == -EAGAIN)
> + goto slow;
> + else if (err)
> + goto err;
> + }
>
> /* The objects are in their final locations, apply the relocations. */
> - if (eb->args->flags & __EXEC_HAS_RELOC) {
> + if (eb->args->flags & __EXEC_HAS_RELOC && first) {
> struct eb_vma *ev;
>
> list_for_each_entry(ev, &eb->relocs, reloc_link) {
> @@ -2211,13 +2214,13 @@ static int eb_relocate_parse(struct i915_execbuffer *eb)
> goto slow;
> }
>
> - if (!err)
> + if (!err && first)
> err = eb_parse(eb);
>
> err:
> if (err == -EDEADLK) {
> - eb_release_vmas(eb, false);
> - err = i915_gem_ww_ctx_backoff(&eb->ww);
> + eb_release_vmas(eb, false, true);
> + err = i915_gem_ww_ctx_backoff(eb->ww);
> if (!err)
> goto retry;
> }
> @@ -2398,7 +2401,7 @@ shadow_batch_pin(struct i915_execbuffer *eb,
> if (IS_ERR(vma))
> return vma;
>
> - err = i915_vma_pin_ww(vma, &eb->ww, 0, 0, flags);
> + err = i915_vma_pin_ww(vma, eb->ww, 0, 0, flags);
> if (err)
> return ERR_PTR(err);
>
> @@ -2412,7 +2415,7 @@ static struct i915_vma *eb_dispatch_secure(struct i915_execbuffer *eb, struct i9
> * batch" bit. Hence we need to pin secure batches into the global gtt.
> * hsw should have this fixed, but bdw mucks it up again. */
> if (eb->batch_flags & I915_DISPATCH_SECURE)
> - return i915_gem_object_ggtt_pin_ww(vma->obj, &eb->ww, NULL, 0, 0, 0);
> + return i915_gem_object_ggtt_pin_ww(vma->obj, eb->ww, NULL, 0, 0, 0);
>
> return NULL;
> }
> @@ -2458,7 +2461,7 @@ static int eb_parse(struct i915_execbuffer *eb)
> eb->batch_pool = pool;
> }
>
> - err = i915_gem_object_lock(pool->obj, &eb->ww);
> + err = i915_gem_object_lock(pool->obj, eb->ww);
> if (err)
> goto err;
>
> @@ -2666,7 +2669,7 @@ static struct i915_request *eb_pin_engine(struct i915_execbuffer *eb, bool throt
> * GGTT space, so do this first before we reserve a seqno for
> * ourselves.
> */
> - err = intel_context_pin_ww(ce, &eb->ww);
> + err = intel_context_pin_ww(ce, eb->ww);
> if (err)
> return ERR_PTR(err);
>
> @@ -3218,7 +3221,8 @@ i915_gem_do_execbuffer(struct drm_device *dev,
> unsigned int batch_number,
> struct dma_fence *in_fence,
> struct dma_fence *exec_fence,
> - struct dma_fence **out_fence)
> + struct dma_fence **out_fence,
> + struct i915_gem_ww_ctx *ww)
> {
> struct drm_i915_private *i915 = to_i915(dev);
> struct i915_execbuffer eb;
> @@ -3239,7 +3243,8 @@ i915_gem_do_execbuffer(struct drm_device *dev,
>
> eb.exec = exec;
> eb.vma = (struct eb_vma *)(exec + args->buffer_count + 1);
> - eb.vma[0].vma = NULL;
> + if (first)
> + eb.vma[0].vma = NULL;
> eb.reloc_pool = eb.batch_pool = NULL;
> eb.reloc_context = NULL;
>
> @@ -3251,6 +3256,7 @@ i915_gem_do_execbuffer(struct drm_device *dev,
> eb.batch_len = args->batch_len;
> eb.trampoline = NULL;
> eb.composite_fence = NULL;
> + eb.ww = ww;
>
> eb.fences = NULL;
> eb.num_fences = 0;
> @@ -3269,9 +3275,14 @@ i915_gem_do_execbuffer(struct drm_device *dev,
> if (err)
> goto err_ext;
>
> - err = eb_create(&eb);
> - if (err)
> - goto err_ext;
> + if (first) {
> + err = eb_create(&eb);
> + if (err)
> + goto err_ext;
> + } else {
> + eb.lut_size = -eb.buffer_count;
> + }
> +
>
> GEM_BUG_ON(!eb.lut_size);
>
> @@ -3286,15 +3297,22 @@ i915_gem_do_execbuffer(struct drm_device *dev,
> if (unlikely(err))
> goto err_context;
>
> - err = eb_lookup_vmas(&eb);
> - if (err) {
> - eb_release_vmas(&eb, true);
> - goto err_engine;
> + if (first) {
> + err = eb_lookup_vmas(&eb);
> + if (err) {
> + eb_release_vmas(&eb, true, true);
> + goto err_engine;
> + }
> +
> + } else {
> + eb.batch = &eb.vma[eb.batch_index];
> }
>
> - i915_gem_ww_ctx_init(&eb.ww, true);
>
> - err = eb_relocate_parse(&eb);
> + if (first)
> + i915_gem_ww_ctx_init(eb.ww, true);
> +
> + err = eb_relocate_parse(&eb, first);
> if (err) {
> /*
> * If the user expects the execobject.offset and
> @@ -3307,7 +3325,8 @@ i915_gem_do_execbuffer(struct drm_device *dev,
> goto err_vma;
> }
>
> - ww_acquire_done(&eb.ww.ctx);
> + if (first)
> + ww_acquire_done(&eb.ww->ctx);
>
> batch = eb.batch->vma;
>
> @@ -3410,11 +3429,12 @@ i915_gem_do_execbuffer(struct drm_device *dev,
> i915_request_put(eb.request);
>
> err_vma:
> - eb_release_vmas(&eb, true);
> + eb_release_vmas(&eb, true, err || last);
> if (eb.trampoline)
> i915_vma_unpin(eb.trampoline);
> WARN_ON(err == -EDEADLK);
> - i915_gem_ww_ctx_fini(&eb.ww);
> + if (err || last)
> + i915_gem_ww_ctx_fini(eb.ww);
>
> if (eb.batch_pool)
> intel_gt_buffer_pool_put(eb.batch_pool);
> @@ -3476,6 +3496,7 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
> const size_t count = args->buffer_count;
> int err;
> struct i915_gem_context *ctx;
> + struct i915_gem_ww_ctx ww;
> struct intel_context *parent = NULL;
> unsigned int num_batches = 1, i;
> bool is_parallel = false;
> @@ -3602,7 +3623,8 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
> 0,
> in_fence,
> exec_fence,
> - out_fences);
> + out_fences,
> + &ww);
>
> for (i = 1; err == 0 && i < num_batches; i++)
> err = i915_gem_do_execbuffer(dev, file, args, exec2_list,
> @@ -3612,7 +3634,8 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
> i,
> NULL,
> NULL,
> - out_fences);
> + out_fences,
> + &ww);
>
> if (is_parallel)
> mutex_unlock(&parent->parallel_submit);
> diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_execbuffer.c
> index 16162fc2782d..710d2700e5b4 100644
> --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_execbuffer.c
> @@ -32,11 +32,11 @@ static int __igt_gpu_reloc(struct i915_execbuffer *eb,
> if (IS_ERR(vma))
> return PTR_ERR(vma);
>
> - err = i915_gem_object_lock(obj, &eb->ww);
> + err = i915_gem_object_lock(obj, eb->ww);
> if (err)
> return err;
>
> - err = i915_vma_pin_ww(vma, &eb->ww, 0, 0, PIN_USER | PIN_HIGH);
> + err = i915_vma_pin_ww(vma, eb->ww, 0, 0, PIN_USER | PIN_HIGH);
> if (err)
> return err;
>
> @@ -106,10 +106,12 @@ static int __igt_gpu_reloc(struct i915_execbuffer *eb,
> static int igt_gpu_reloc(void *arg)
> {
> struct i915_execbuffer eb;
> + struct i915_gem_ww_ctx ww;
> struct drm_i915_gem_object *scratch;
> int err = 0;
> u32 *map;
>
> + eb.ww = &ww;
> eb.i915 = arg;
>
> scratch = i915_gem_object_create_internal(eb.i915, 4096);
> @@ -141,20 +143,20 @@ static int igt_gpu_reloc(void *arg)
> eb.reloc_pool = NULL;
> eb.reloc_context = NULL;
>
> - i915_gem_ww_ctx_init(&eb.ww, false);
> + i915_gem_ww_ctx_init(eb.ww, false);
> retry:
> - err = intel_context_pin_ww(eb.context, &eb.ww);
> + err = intel_context_pin_ww(eb.context, eb.ww);
> if (!err) {
> err = __igt_gpu_reloc(&eb, scratch);
>
> intel_context_unpin(eb.context);
> }
> if (err == -EDEADLK) {
> - err = i915_gem_ww_ctx_backoff(&eb.ww);
> + err = i915_gem_ww_ctx_backoff(eb.ww);
> if (!err)
> goto retry;
> }
> - i915_gem_ww_ctx_fini(&eb.ww);
> + i915_gem_ww_ctx_fini(eb.ww);
>
> if (eb.reloc_pool)
> intel_gt_buffer_pool_put(eb.reloc_pool);
> --
> 2.28.0
>

--
Daniel Vetter
Software Engineer, Intel Corporation