Re: [Intel-gfx] [PATCH v15 16/23] drm/shmem-helper: Use kref for vmap_use_count
On 8/28/23 13:00, Boris Brezillon wrote: > On Sun, 27 Aug 2023 20:54:42 +0300 > Dmitry Osipenko wrote: > >> Use kref helper for vmap_use_count to make refcounting consistent with >> pages_use_count and pages_pin_count that use kref. This will allow to >> optimize unlocked vmappings by skipping reservation locking if refcnt > 1. > > The core is taking the resv lock before calling ->v[un]map(), so > switching to a kref sounds a bit premature/useless, unless there are > plans to delegate the locking to the drivers. The only thing it brings > is standard overflow/underflow checks. Not really sure it's worth > transitioning to a kref for this field until we have a real use case. The overflow checks worth transitioning. I'll mention them in the commit message for v16. -- Best regards, Dmitry
Re: [Intel-gfx] [PATCH v15 16/23] drm/shmem-helper: Use kref for vmap_use_count
On Sun, 27 Aug 2023 20:54:42 +0300
Dmitry Osipenko wrote:
> Use kref helper for vmap_use_count to make refcounting consistent with
> pages_use_count and pages_pin_count that use kref. This will allow to
> optimize unlocked vmappings by skipping reservation locking if refcnt > 1.
The core is taking the resv lock before calling ->v[un]map(), so
switching to a kref sounds a bit premature/useless, unless there are
plans to delegate the locking to the drivers. The only thing it brings
is standard overflow/underflow checks. Not really sure it's worth
transitioning to a kref for this field until we have a real use case.
>
> Suggested-by: Boris Brezillon
> Signed-off-by: Dmitry Osipenko
> ---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 37 ++
> include/drm/drm_gem_shmem_helper.h | 2 +-
> 2 files changed, 21 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
> b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 17a0177acb5d..d96fee3d6166 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -144,7 +144,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object
> *shmem)
> } else if (!shmem->imported_sgt) {
> dma_resv_lock(shmem->base.resv, NULL);
>
> - drm_WARN_ON(obj->dev, shmem->vmap_use_count);
> + drm_WARN_ON(obj->dev, kref_read(>vmap_use_count));
>
> if (shmem->sgt) {
> dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
> @@ -359,23 +359,25 @@ int drm_gem_shmem_vmap_locked(struct
> drm_gem_shmem_object *shmem,
>
> dma_resv_assert_held(shmem->base.resv);
>
> - if (shmem->vmap_use_count++ > 0) {
> + if (kref_get_unless_zero(>vmap_use_count)) {
> iosys_map_set_vaddr(map, shmem->vaddr);
> return 0;
> }
>
> ret = drm_gem_shmem_pin_locked(shmem);
> if (ret)
> - goto err_zero_use;
> + return ret;
>
> if (shmem->map_wc)
> prot = pgprot_writecombine(prot);
> shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
> VM_MAP, prot);
> - if (!shmem->vaddr)
> + if (!shmem->vaddr) {
> ret = -ENOMEM;
> - else
> + } else {
> iosys_map_set_vaddr(map, shmem->vaddr);
> + kref_init(>vmap_use_count);
> + }
> }
>
> if (ret) {
> @@ -388,13 +390,22 @@ int drm_gem_shmem_vmap_locked(struct
> drm_gem_shmem_object *shmem,
> err_put_pages:
> if (!obj->import_attach)
> drm_gem_shmem_unpin_locked(shmem);
> -err_zero_use:
> - shmem->vmap_use_count = 0;
>
> return ret;
> }
> EXPORT_SYMBOL_GPL(drm_gem_shmem_vmap_locked);
>
> +static void drm_gem_shmem_kref_vunmap(struct kref *kref)
> +{
> + struct drm_gem_shmem_object *shmem;
> +
> + shmem = container_of(kref, struct drm_gem_shmem_object,
> + vmap_use_count);
> +
> + vunmap(shmem->vaddr);
> + drm_gem_shmem_unpin_locked(shmem);
> +}
> +
> /*
> * drm_gem_shmem_vunmap_locked - Unmap a virtual mapping for a shmem GEM
> object
> * @shmem: shmem GEM object
> @@ -416,15 +427,7 @@ void drm_gem_shmem_vunmap_locked(struct
> drm_gem_shmem_object *shmem,
> dma_buf_vunmap(obj->import_attach->dmabuf, map);
> } else {
> dma_resv_assert_held(shmem->base.resv);
> -
> - if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
> - return;
> -
> - if (--shmem->vmap_use_count > 0)
> - return;
> -
> - vunmap(shmem->vaddr);
> - drm_gem_shmem_unpin_locked(shmem);
> + kref_put(>vmap_use_count, drm_gem_shmem_kref_vunmap);
> }
>
> shmem->vaddr = NULL;
> @@ -663,7 +666,7 @@ void drm_gem_shmem_print_info(const struct
> drm_gem_shmem_object *shmem,
> return;
>
> drm_printf_indent(p, indent, "pages_use_count=%u\n",
> kref_read(>pages_use_count));
> - drm_printf_indent(p, indent, "vmap_use_count=%u\n",
> shmem->vmap_use_count);
> + drm_printf_indent(p, indent, "vmap_use_count=%u\n",
> kref_read(>vmap_use_count));
> drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
> }
> EXPORT_SYMBOL_GPL(drm_gem_shmem_print_info);
> diff --git a/include/drm/drm_gem_shmem_helper.h
> b/include/drm/drm_gem_shmem_helper.h
> index 400ecd63f45f..0e0ccd380f66 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -81,7 +81,7 @@ struct drm_gem_shmem_object {
>* Reference count on the virtual address.
>* The address are un-mapped when the count reaches zero.
>*/
> - unsigned int vmap_use_count;
> + struct kref
[Intel-gfx] [PATCH v15 16/23] drm/shmem-helper: Use kref for vmap_use_count
Use kref helper for vmap_use_count to make refcounting consistent with
pages_use_count and pages_pin_count that use kref. This will allow to
optimize unlocked vmappings by skipping reservation locking if refcnt > 1.
Suggested-by: Boris Brezillon
Signed-off-by: Dmitry Osipenko
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 37 ++
include/drm/drm_gem_shmem_helper.h | 2 +-
2 files changed, 21 insertions(+), 18 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 17a0177acb5d..d96fee3d6166 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -144,7 +144,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
} else if (!shmem->imported_sgt) {
dma_resv_lock(shmem->base.resv, NULL);
- drm_WARN_ON(obj->dev, shmem->vmap_use_count);
+ drm_WARN_ON(obj->dev, kref_read(>vmap_use_count));
if (shmem->sgt) {
dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
@@ -359,23 +359,25 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object
*shmem,
dma_resv_assert_held(shmem->base.resv);
- if (shmem->vmap_use_count++ > 0) {
+ if (kref_get_unless_zero(>vmap_use_count)) {
iosys_map_set_vaddr(map, shmem->vaddr);
return 0;
}
ret = drm_gem_shmem_pin_locked(shmem);
if (ret)
- goto err_zero_use;
+ return ret;
if (shmem->map_wc)
prot = pgprot_writecombine(prot);
shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
VM_MAP, prot);
- if (!shmem->vaddr)
+ if (!shmem->vaddr) {
ret = -ENOMEM;
- else
+ } else {
iosys_map_set_vaddr(map, shmem->vaddr);
+ kref_init(>vmap_use_count);
+ }
}
if (ret) {
@@ -388,13 +390,22 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object
*shmem,
err_put_pages:
if (!obj->import_attach)
drm_gem_shmem_unpin_locked(shmem);
-err_zero_use:
- shmem->vmap_use_count = 0;
return ret;
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_vmap_locked);
+static void drm_gem_shmem_kref_vunmap(struct kref *kref)
+{
+ struct drm_gem_shmem_object *shmem;
+
+ shmem = container_of(kref, struct drm_gem_shmem_object,
+vmap_use_count);
+
+ vunmap(shmem->vaddr);
+ drm_gem_shmem_unpin_locked(shmem);
+}
+
/*
* drm_gem_shmem_vunmap_locked - Unmap a virtual mapping for a shmem GEM object
* @shmem: shmem GEM object
@@ -416,15 +427,7 @@ void drm_gem_shmem_vunmap_locked(struct
drm_gem_shmem_object *shmem,
dma_buf_vunmap(obj->import_attach->dmabuf, map);
} else {
dma_resv_assert_held(shmem->base.resv);
-
- if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
- return;
-
- if (--shmem->vmap_use_count > 0)
- return;
-
- vunmap(shmem->vaddr);
- drm_gem_shmem_unpin_locked(shmem);
+ kref_put(>vmap_use_count, drm_gem_shmem_kref_vunmap);
}
shmem->vaddr = NULL;
@@ -663,7 +666,7 @@ void drm_gem_shmem_print_info(const struct
drm_gem_shmem_object *shmem,
return;
drm_printf_indent(p, indent, "pages_use_count=%u\n",
kref_read(>pages_use_count));
- drm_printf_indent(p, indent, "vmap_use_count=%u\n",
shmem->vmap_use_count);
+ drm_printf_indent(p, indent, "vmap_use_count=%u\n",
kref_read(>vmap_use_count));
drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_print_info);
diff --git a/include/drm/drm_gem_shmem_helper.h
b/include/drm/drm_gem_shmem_helper.h
index 400ecd63f45f..0e0ccd380f66 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -81,7 +81,7 @@ struct drm_gem_shmem_object {
* Reference count on the virtual address.
* The address are un-mapped when the count reaches zero.
*/
- unsigned int vmap_use_count;
+ struct kref vmap_use_count;
/**
* @got_sgt:
--
2.41.0
