Thank you for updating the docs Matthew. I am looking forward to this
patch landing.
On Fri, Dec 16, 2022 at 10:35 PM Matthew Auld <matthew.auld@xxxxxxxxx> wrote:
>
> The catch-all evict can fail due to object lock contention, since it
> only goes as far as trylocking the object, due to us already holding the
> vm->mutex. Doing a full object lock here can deadlock, since the
> vm->mutex is always our inner lock. Add another execbuf pass which drops
> the vm->mutex and then tries to grab the object will the full lock,
> before then retrying the eviction. This should be good enough for now to
> fix the immediate regression with userspace seeing -ENOSPC from execbuf
> due to contended object locks during GTT eviction.
>
> v2 (Mani)
> - Also revamp the docs for the different passes.
>
> Testcase: igt@gem_ppgtt@shrink-vs-evict-*
> Fixes: 7e00897be8bf ("drm/i915: Add object locking to i915_gem_evict_for_node and i915_gem_evict_something, v2.")
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/7627
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/7570
> References: https://bugzilla.mozilla.org/show_bug.cgi?id=1779558
> Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> Cc: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> Cc: Mani Milani <mani@xxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.18+
> Reviewed-by: Mani Milani <mani@xxxxxxxxxxxx>
> Tested-by: Mani Milani <mani@xxxxxxxxxxxx>
> ---
> .../gpu/drm/i915/gem/i915_gem_execbuffer.c | 59 +++++++++++++++----
> drivers/gpu/drm/i915/gem/i915_gem_mman.c | 2 +-
> drivers/gpu/drm/i915/i915_gem_evict.c | 37 ++++++++----
> drivers/gpu/drm/i915/i915_gem_evict.h | 4 +-
> drivers/gpu/drm/i915/i915_vma.c | 2 +-
> .../gpu/drm/i915/selftests/i915_gem_evict.c | 4 +-
> 6 files changed, 82 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 192bb3f10733..f98600ca7557 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -733,32 +733,69 @@ static int eb_reserve(struct i915_execbuffer *eb)
> bool unpinned;
>
> /*
> - * Attempt to pin all of the buffers into the GTT.
> - * This is done in 2 phases:
> + * We have one more buffers that we couldn't bind, which could be due to
> + * various reasons. To resolve this we have 4 passes, with every next
> + * level turning the screws tighter:
> *
> - * 1. Unbind all objects that do not match the GTT constraints for
> - * the execbuffer (fenceable, mappable, alignment etc).
> - * 2. Bind new objects.
> + * 0. Unbind all objects that do not match the GTT constraints for the
> + * execbuffer (fenceable, mappable, alignment etc). Bind all new
> + * objects. This avoids unnecessary unbinding of later objects in order
> + * to make room for the earlier objects *unless* we need to defragment.
> *
> - * This avoid unnecessary unbinding of later objects in order to make
> - * room for the earlier objects *unless* we need to defragment.
> + * 1. Reorder the buffers, where objects with the most restrictive
> + * placement requirements go first (ignoring fixed location buffers for
> + * now). For example, objects needing the mappable aperture (the first
> + * 256M of GTT), should go first vs objects that can be placed just
> + * about anywhere. Repeat the previous pass.
> *
> - * Defragmenting is skipped if all objects are pinned at a fixed location.
> + * 2. Consider buffers that are pinned at a fixed location. Also try to
> + * evict the entire VM this time, leaving only objects that we were
> + * unable to lock. Try again to bind the buffers. (still using the new
> + * buffer order).
> + *
> + * 3. We likely have object lock contention for one or more stubborn
> + * objects in the VM, for which we need to evict to make forward
> + * progress (perhaps we are fighting the shrinker?). When evicting the
> + * VM this time around, anything that we can't lock we now track using
> + * the busy_bo, using the full lock (after dropping the vm->mutex to
> + * prevent deadlocks), instead of trylock. We then continue to evict the
> + * VM, this time with the stubborn object locked, which we can now
> + * hopefully unbind (if still bound in the VM). Repeat until the VM is
> + * evicted. Finally we should be able bind everything.
> */
> - for (pass = 0; pass <= 2; pass++) {
> + for (pass = 0; pass <= 3; pass++) {
> int pin_flags = PIN_USER | PIN_VALIDATE;
>
> if (pass == 0)
> pin_flags |= PIN_NONBLOCK;
>
> if (pass >= 1)
> - unpinned = eb_unbind(eb, pass == 2);
> + unpinned = eb_unbind(eb, pass >= 2);
>
> if (pass == 2) {
> err = mutex_lock_interruptible(&eb->context->vm->mutex);
> if (!err) {
> - err = i915_gem_evict_vm(eb->context->vm, &eb->ww);
> + err = i915_gem_evict_vm(eb->context->vm, &eb->ww, NULL);
> + mutex_unlock(&eb->context->vm->mutex);
> + }
> + if (err)
> + return err;
> + }
> +
> + if (pass == 3) {
> +retry:
> + err = mutex_lock_interruptible(&eb->context->vm->mutex);
> + if (!err) {
> + struct drm_i915_gem_object *busy_bo = NULL;
> +
> + err = i915_gem_evict_vm(eb->context->vm, &eb->ww, &busy_bo);
> mutex_unlock(&eb->context->vm->mutex);
> + if (err && busy_bo) {
> + err = i915_gem_object_lock(busy_bo, &eb->ww);
> + i915_gem_object_put(busy_bo);
> + if (!err)
> + goto retry;
> + }
> }
> if (err)
> return err;
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> index d73ba0f5c4c5..4f69bff63068 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> @@ -369,7 +369,7 @@ static vm_fault_t vm_fault_gtt(struct vm_fault *vmf)
> if (vma == ERR_PTR(-ENOSPC)) {
> ret = mutex_lock_interruptible(&ggtt->vm.mutex);
> if (!ret) {
> - ret = i915_gem_evict_vm(&ggtt->vm, &ww);
> + ret = i915_gem_evict_vm(&ggtt->vm, &ww, NULL);
> mutex_unlock(&ggtt->vm.mutex);
> }
> if (ret)
> diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
> index 4cfe36b0366b..c02ebd6900ae 100644
> --- a/drivers/gpu/drm/i915/i915_gem_evict.c
> +++ b/drivers/gpu/drm/i915/i915_gem_evict.c
> @@ -441,6 +441,11 @@ int i915_gem_evict_for_node(struct i915_address_space *vm,
> * @vm: Address space to cleanse
> * @ww: An optional struct i915_gem_ww_ctx. If not NULL, i915_gem_evict_vm
> * will be able to evict vma's locked by the ww as well.
> + * @busy_bo: Optional pointer to struct drm_i915_gem_object. If not NULL, then
> + * in the event i915_gem_evict_vm() is unable to trylock an object for eviction,
> + * then @busy_bo will point to it. -EBUSY is also returned. The caller must drop
> + * the vm->mutex, before trying again to acquire the contended lock. The caller
> + * also owns a reference to the object.
> *
> * This function evicts all vmas from a vm.
> *
> @@ -450,7 +455,8 @@ int i915_gem_evict_for_node(struct i915_address_space *vm,
> * To clarify: This is for freeing up virtual address space, not for freeing
> * memory in e.g. the shrinker.
> */
> -int i915_gem_evict_vm(struct i915_address_space *vm, struct i915_gem_ww_ctx *ww)
> +int i915_gem_evict_vm(struct i915_address_space *vm, struct i915_gem_ww_ctx *ww,
> + struct drm_i915_gem_object **busy_bo)
> {
> int ret = 0;
>
> @@ -482,15 +488,22 @@ int i915_gem_evict_vm(struct i915_address_space *vm, struct i915_gem_ww_ctx *ww)
> * the resv is shared among multiple objects, we still
> * need the object ref.
> */
> - if (dying_vma(vma) ||
> + if (!i915_gem_object_get_rcu(vma->obj) ||
> (ww && (dma_resv_locking_ctx(vma->obj->base.resv) == &ww->ctx))) {
> __i915_vma_pin(vma);
> list_add(&vma->evict_link, &locked_eviction_list);
> continue;
> }
>
> - if (!i915_gem_object_trylock(vma->obj, ww))
> + if (!i915_gem_object_trylock(vma->obj, ww)) {
> + if (busy_bo) {
> + *busy_bo = vma->obj; /* holds ref */
> + ret = -EBUSY;
> + break;
> + }
> + i915_gem_object_put(vma->obj);
> continue;
> + }
>
> __i915_vma_pin(vma);
> list_add(&vma->evict_link, &eviction_list);
> @@ -498,25 +511,29 @@ int i915_gem_evict_vm(struct i915_address_space *vm, struct i915_gem_ww_ctx *ww)
> if (list_empty(&eviction_list) && list_empty(&locked_eviction_list))
> break;
>
> - ret = 0;
> /* Unbind locked objects first, before unlocking the eviction_list */
> list_for_each_entry_safe(vma, vn, &locked_eviction_list, evict_link) {
> __i915_vma_unpin(vma);
>
> - if (ret == 0)
> + if (ret == 0) {
> ret = __i915_vma_unbind(vma);
> - if (ret != -EINTR) /* "Get me out of here!" */
> - ret = 0;
> + if (ret != -EINTR) /* "Get me out of here!" */
> + ret = 0;
> + }
> + if (!dying_vma(vma))
> + i915_gem_object_put(vma->obj);
> }
>
> list_for_each_entry_safe(vma, vn, &eviction_list, evict_link) {
> __i915_vma_unpin(vma);
> - if (ret == 0)
> + if (ret == 0) {
> ret = __i915_vma_unbind(vma);
> - if (ret != -EINTR) /* "Get me out of here!" */
> - ret = 0;
> + if (ret != -EINTR) /* "Get me out of here!" */
> + ret = 0;
> + }
>
> i915_gem_object_unlock(vma->obj);
> + i915_gem_object_put(vma->obj);
> }
> } while (ret == 0);
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_evict.h b/drivers/gpu/drm/i915/i915_gem_evict.h
> index e593c530f9bd..bf0ee0e4fe60 100644
> --- a/drivers/gpu/drm/i915/i915_gem_evict.h
> +++ b/drivers/gpu/drm/i915/i915_gem_evict.h
> @@ -11,6 +11,7 @@
> struct drm_mm_node;
> struct i915_address_space;
> struct i915_gem_ww_ctx;
> +struct drm_i915_gem_object;
>
> int __must_check i915_gem_evict_something(struct i915_address_space *vm,
> struct i915_gem_ww_ctx *ww,
> @@ -23,6 +24,7 @@ int __must_check i915_gem_evict_for_node(struct i915_address_space *vm,
> struct drm_mm_node *node,
> unsigned int flags);
> int i915_gem_evict_vm(struct i915_address_space *vm,
> - struct i915_gem_ww_ctx *ww);
> + struct i915_gem_ww_ctx *ww,
> + struct drm_i915_gem_object **busy_bo);
>
> #endif /* __I915_GEM_EVICT_H__ */
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index 34f0e6c923c2..7d044888ac33 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -1599,7 +1599,7 @@ static int __i915_ggtt_pin(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
> * locked objects when called from execbuf when pinning
> * is removed. This would probably regress badly.
> */
> - i915_gem_evict_vm(vm, NULL);
> + i915_gem_evict_vm(vm, NULL, NULL);
> mutex_unlock(&vm->mutex);
> }
> } while (1);
> diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_evict.c b/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> index 8c6517d29b8e..37068542aafe 100644
> --- a/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> +++ b/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> @@ -344,7 +344,7 @@ static int igt_evict_vm(void *arg)
>
> /* Everything is pinned, nothing should happen */
> mutex_lock(&ggtt->vm.mutex);
> - err = i915_gem_evict_vm(&ggtt->vm, NULL);
> + err = i915_gem_evict_vm(&ggtt->vm, NULL, NULL);
> mutex_unlock(&ggtt->vm.mutex);
> if (err) {
> pr_err("i915_gem_evict_vm on a full GGTT returned err=%d]\n",
> @@ -356,7 +356,7 @@ static int igt_evict_vm(void *arg)
>
> for_i915_gem_ww(&ww, err, false) {
> mutex_lock(&ggtt->vm.mutex);
> - err = i915_gem_evict_vm(&ggtt->vm, &ww);
> + err = i915_gem_evict_vm(&ggtt->vm, &ww, NULL);
> mutex_unlock(&ggtt->vm.mutex);
> }
>
> --
> 2.38.1
>
