| Message ID | 1399440098-17378-4-git-send-email-benjamin.widawsky@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, May 06, 2014 at 10:21:33PM -0700, Ben Widawsky wrote: > AFAICT, it's impossible to actually infinitely retry the allocation in > our current code. However, a small oversight on my part, slight bug, or > future bug, could easily change that. > > To avoid a potential breakage, a simple retry variable of 16 bits will > help us prevent infinitely running. > > Retry is limited to 100 as a mostly random number. Some consideration > about stack usage was taken into account. As an example, if we allowed > 256 retries on a 32b arch (and my memory serves that all arguments are > passed on the stack for such architectures), thats 33 bytes * 256 > retries + (fudge for return address and such)... it's way more than we > want to use already. 64b architectures might be slightly better, since > 6? of the first args will get passed through registers, but it's still > bad. > > If anything, we might want to do way less than 100, like 3. > > Signed-off-by: Ben Widawsky <ben@bwidawsk.net> So you replace the retry loop with a tailrecursive version in patch 2 and then add duct-tape later on here? Nope. -Daniel > --- > drivers/gpu/drm/i915/i915_gem.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index b6965a2..de98b26 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -3216,6 +3216,7 @@ static void i915_gem_verify_gtt(struct drm_device *dev) > #endif > } > > +#define MAX_VMA_FIND_RETRY 100 > static int > i915_gem_find_vm_space(struct i915_address_space *vm, > struct drm_mm_node *node, > @@ -3224,7 +3225,8 @@ i915_gem_find_vm_space(struct i915_address_space *vm, > unsigned long color, > unsigned long start, > unsigned long end, > - uint32_t flags) > + uint32_t flags, > + uint8_t retry) > { > int ret; > ret = drm_mm_insert_node_in_range_generic(&vm->mm, node, > @@ -3232,7 +3234,7 @@ i915_gem_find_vm_space(struct i915_address_space *vm, > start, end, > DRM_MM_SEARCH_DEFAULT, > DRM_MM_CREATE_DEFAULT); > - if (ret) { > + if (ret && (retry < MAX_VMA_FIND_RETRY)) { > if (WARN_ON(ret != -ENOSPC)) > return ret; > > @@ -3241,7 +3243,8 @@ i915_gem_find_vm_space(struct i915_address_space *vm, > if (ret == 0) > return i915_gem_find_vm_space(vm, node, > size, align, color, > - start, end, flags); > + start, end, flags, > + retry++); > } > > return ret; > @@ -3306,8 +3309,9 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj, > if (IS_ERR(vma)) > goto err_unpin; > > - ret = i915_gem_find_vm_space(vm, &vma->node, size, alignment, > - obj->cache_level, 0, gtt_max, flags); > + ret = i915_gem_find_vm_space(vm, &vma->node, > + size, alignment, obj->cache_level, > + 0, gtt_max, flags, 1); > if (ret) > goto err_free_vma; > > -- > 1.9.2 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
On Wed, May 07, 2014 at 09:49:57AM +0200, Daniel Vetter wrote: > On Tue, May 06, 2014 at 10:21:33PM -0700, Ben Widawsky wrote: > > AFAICT, it's impossible to actually infinitely retry the allocation in > > our current code. However, a small oversight on my part, slight bug, or > > future bug, could easily change that. > > > > To avoid a potential breakage, a simple retry variable of 16 bits will > > help us prevent infinitely running. > > > > Retry is limited to 100 as a mostly random number. Some consideration > > about stack usage was taken into account. As an example, if we allowed > > 256 retries on a 32b arch (and my memory serves that all arguments are > > passed on the stack for such architectures), thats 33 bytes * 256 > > retries + (fudge for return address and such)... it's way more than we > > want to use already. 64b architectures might be slightly better, since > > 6? of the first args will get passed through registers, but it's still > > bad. > > > > If anything, we might want to do way less than 100, like 3. > > > > Signed-off-by: Ben Widawsky <ben@bwidawsk.net> > > So you replace the retry loop with a tailrecursive version in patch 2 and > then add duct-tape later on here? Nope. > -Daniel > I feel like you're implying the retry loop will end, ever. The retry timeout should probably come first though, I Agree with that much. > > --- > > drivers/gpu/drm/i915/i915_gem.c | 14 +++++++++----- > > 1 file changed, 9 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > > index b6965a2..de98b26 100644 > > --- a/drivers/gpu/drm/i915/i915_gem.c > > +++ b/drivers/gpu/drm/i915/i915_gem.c > > @@ -3216,6 +3216,7 @@ static void i915_gem_verify_gtt(struct drm_device *dev) > > #endif > > } > > > > +#define MAX_VMA_FIND_RETRY 100 > > static int > > i915_gem_find_vm_space(struct i915_address_space *vm, > > struct drm_mm_node *node, > > @@ -3224,7 +3225,8 @@ i915_gem_find_vm_space(struct i915_address_space *vm, > > unsigned long color, > > unsigned long start, > > unsigned long end, > > - uint32_t flags) > > + uint32_t flags, > > + uint8_t retry) > > { > > int ret; > > ret = drm_mm_insert_node_in_range_generic(&vm->mm, node, > > @@ -3232,7 +3234,7 @@ i915_gem_find_vm_space(struct i915_address_space *vm, > > start, end, > > DRM_MM_SEARCH_DEFAULT, > > DRM_MM_CREATE_DEFAULT); > > - if (ret) { > > + if (ret && (retry < MAX_VMA_FIND_RETRY)) { > > if (WARN_ON(ret != -ENOSPC)) > > return ret; > > > > @@ -3241,7 +3243,8 @@ i915_gem_find_vm_space(struct i915_address_space *vm, > > if (ret == 0) > > return i915_gem_find_vm_space(vm, node, > > size, align, color, > > - start, end, flags); > > + start, end, flags, > > + retry++); > > } > > > > return ret; > > @@ -3306,8 +3309,9 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj, > > if (IS_ERR(vma)) > > goto err_unpin; > > > > - ret = i915_gem_find_vm_space(vm, &vma->node, size, alignment, > > - obj->cache_level, 0, gtt_max, flags); > > + ret = i915_gem_find_vm_space(vm, &vma->node, > > + size, alignment, obj->cache_level, > > + 0, gtt_max, flags, 1); > > if (ret) > > goto err_free_vma; > > > > -- > > 1.9.2 > > > > _______________________________________________ > > Intel-gfx mailing list > > Intel-gfx@lists.freedesktop.org > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx > > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index b6965a2..de98b26 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -3216,6 +3216,7 @@ static void i915_gem_verify_gtt(struct drm_device *dev) #endif } +#define MAX_VMA_FIND_RETRY 100 static int i915_gem_find_vm_space(struct i915_address_space *vm, struct drm_mm_node *node, @@ -3224,7 +3225,8 @@ i915_gem_find_vm_space(struct i915_address_space *vm, unsigned long color, unsigned long start, unsigned long end, - uint32_t flags) + uint32_t flags, + uint8_t retry) { int ret; ret = drm_mm_insert_node_in_range_generic(&vm->mm, node, @@ -3232,7 +3234,7 @@ i915_gem_find_vm_space(struct i915_address_space *vm, start, end, DRM_MM_SEARCH_DEFAULT, DRM_MM_CREATE_DEFAULT); - if (ret) { + if (ret && (retry < MAX_VMA_FIND_RETRY)) { if (WARN_ON(ret != -ENOSPC)) return ret; @@ -3241,7 +3243,8 @@ i915_gem_find_vm_space(struct i915_address_space *vm, if (ret == 0) return i915_gem_find_vm_space(vm, node, size, align, color, - start, end, flags); + start, end, flags, + retry++); } return ret; @@ -3306,8 +3309,9 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj, if (IS_ERR(vma)) goto err_unpin; - ret = i915_gem_find_vm_space(vm, &vma->node, size, alignment, - obj->cache_level, 0, gtt_max, flags); + ret = i915_gem_find_vm_space(vm, &vma->node, + size, alignment, obj->cache_level, + 0, gtt_max, flags, 1); if (ret) goto err_free_vma;
AFAICT, it's impossible to actually infinitely retry the allocation in our current code. However, a small oversight on my part, slight bug, or future bug, could easily change that. To avoid a potential breakage, a simple retry variable of 16 bits will help us prevent infinitely running. Retry is limited to 100 as a mostly random number. Some consideration about stack usage was taken into account. As an example, if we allowed 256 retries on a 32b arch (and my memory serves that all arguments are passed on the stack for such architectures), thats 33 bytes * 256 retries + (fudge for return address and such)... it's way more than we want to use already. 64b architectures might be slightly better, since 6? of the first args will get passed through registers, but it's still bad. If anything, we might want to do way less than 100, like 3. Signed-off-by: Ben Widawsky <ben@bwidawsk.net> --- drivers/gpu/drm/i915/i915_gem.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)