Before we instantiate/pin the backing store for our use, we can prepopulate the shmemfs filp efficiently using the a write into the pagecache. We avoid the penalty of instantiating all the pages, important if the user is just writing to a few and never uses the object on the GPU, and using a direct write into shmemfs allows it to avoid the cost of retrieving a page (either swapin or clearing-before-use) before it is overwritten.
This can be extended later to provide additional specialisation for other backends (other than shmemfs). References: https://bugs.freedesktop.org/show_bug.cgi?id=99107 Signed-off-by: Chris Wilson <[email protected]> Cc: Matthew Auld <[email protected]> Cc: Joonas Lahtinen <[email protected]> Cc: Mika Kuoppala <[email protected]> --- drivers/gpu/drm/i915/i915_gem.c | 78 ++++++++++++++++++++++++++++++++++ drivers/gpu/drm/i915/i915_gem_object.h | 3 ++ 2 files changed, 81 insertions(+) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 7c20601fe1de..73d5cee23dd7 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -1452,6 +1452,12 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data, trace_i915_gem_object_pwrite(obj, args->offset, args->size); + ret = -ENODEV; + if (obj->ops->pwrite) + ret = obj->ops->pwrite(obj, args); + if (ret != -ENODEV) + goto err; + ret = i915_gem_object_wait(obj, I915_WAIT_INTERRUPTIBLE | I915_WAIT_ALL, @@ -2575,6 +2581,75 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj, goto out_unlock; } +static int +i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj, + const struct drm_i915_gem_pwrite *arg) +{ + struct address_space *mapping = obj->base.filp->f_mapping; + char __user *user_data = u64_to_user_ptr(arg->data_ptr); + u64 remain, offset; + unsigned int pg; + + /* Before we instantiate/pin the backing store for our use, we + * can prepopulate the shmemfs filp efficiently using the a + * write into the pagecache. We avoid the penalty of instantiating + * all the pages, important if the user is just writing to a few + * and never uses the object on the GPU, and using a direct write + * into shmemfs allows it to avoid the cost of retrieving a page + * (either swapin or clearing-before-use) before it is overwritten. + */ + if (READ_ONCE(obj->mm.pages)) + return -ENODEV; + + /* Before the pages are instantioted the object is treated as being + * in the CPU domain. The pages will be clflushed as required before + * use, and we can freely write into the pages directly. If userspace + * races pwrite with any other operation; corruption will ensue - + * that is userspace's perogative! + */ + + remain = arg->size; + offset = arg->offset; + pg = offset_in_page(offset); + + do { + unsigned int len, unwritten; + struct page *page; + void *data, *vaddr; + int err; + + len = PAGE_SIZE - pg; + if (len > remain) + len = remain; + + err = pagecache_write_begin(obj->base.filp, mapping, + offset, len, + 0, &page, &data); + if (err < 0) + return err; + + vaddr = kmap(page); + unwritten = copy_from_user(vaddr + pg, user_data, len); + kunmap(page); + + err = pagecache_write_end(obj->base.filp, mapping, offset, + len, len - unwritten, + page, data); + if (err < 0) + return err; + + if (unwritten) + return -EFAULT; + + remain -= len; + user_data += len; + offset += len; + pg = 0; + } while (remain); + + return 0; +} + static bool ban_context(const struct i915_gem_context *ctx) { return (i915_gem_context_is_bannable(ctx) && @@ -3991,8 +4066,11 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj, static const struct drm_i915_gem_object_ops i915_gem_object_ops = { .flags = I915_GEM_OBJECT_HAS_STRUCT_PAGE | I915_GEM_OBJECT_IS_SHRINKABLE, + .get_pages = i915_gem_object_get_pages_gtt, .put_pages = i915_gem_object_put_pages_gtt, + + .pwrite = i915_gem_object_pwrite_gtt, }; struct drm_i915_gem_object * diff --git a/drivers/gpu/drm/i915/i915_gem_object.h b/drivers/gpu/drm/i915/i915_gem_object.h index 33b0dc4782a9..d26155e0a026 100644 --- a/drivers/gpu/drm/i915/i915_gem_object.h +++ b/drivers/gpu/drm/i915/i915_gem_object.h @@ -56,6 +56,9 @@ struct drm_i915_gem_object_ops { struct sg_table *(*get_pages)(struct drm_i915_gem_object *); void (*put_pages)(struct drm_i915_gem_object *, struct sg_table *); + int (*pwrite)(struct drm_i915_gem_object *, + const struct drm_i915_gem_pwrite *); + int (*dmabuf_export)(struct drm_i915_gem_object *); void (*release)(struct drm_i915_gem_object *); }; -- 2.11.0 _______________________________________________ Intel-gfx mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/intel-gfx
