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Improve clarity of MemoryTypeFilter docs (#2428)
* Make the combination disclaimers **impossible** to miss * Add headings to the examples for improved visibility * Update vulkano/src/memory/allocator/mod.rs Co-authored-by: Rua <ruawhitepaw@gmail.com> --------- Co-authored-by: Rua <ruawhitepaw@gmail.com>
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@ -367,6 +367,8 @@ impl Debug for dyn MemoryAllocator {
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///
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/// # Examples
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///
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/// #### Direct device access only
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///
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/// For resources that the device frequently accesses, e.g. textures, render targets, or
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/// intermediary buffers, you want device-local memory without any host access:
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///
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@ -396,8 +398,10 @@ impl Debug for dyn MemoryAllocator {
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/// .unwrap();
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/// ```
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///
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/// #### Sequential writes from host, indirect device access
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///
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/// For staging, the resource is only ever written to sequentially. Also, since the device will
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/// only read the staging resourse once, it would yield no benefit to place it in device-local
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/// only read the staging resource once, it would yield no benefit to place it in device-local
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/// memory, in fact it would be wasteful. Therefore, it's best to put it in host-local memory:
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///
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/// ```
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@ -425,6 +429,8 @@ impl Debug for dyn MemoryAllocator {
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/// # let staging_buffer: vulkano::buffer::Subbuffer<u32> = staging_buffer;
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/// ```
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///
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/// #### Sequential writes from host, direct device access
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///
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/// For resources that the device accesses directly, aka a buffer/image used for anything other
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/// than transfers, it's probably best to put it in device-local memory:
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///
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@ -453,6 +459,8 @@ impl Debug for dyn MemoryAllocator {
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/// # let uniform_buffer: vulkano::buffer::Subbuffer<u32> = uniform_buffer;
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/// ```
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///
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/// #### Readback to host
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///
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/// For readback, e.g. getting the results of a compute shader back to the host:
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///
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/// ```
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@ -487,7 +495,9 @@ pub struct MemoryTypeFilter {
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}
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impl MemoryTypeFilter {
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/// Prefers picking a memory type with the [`DEVICE_LOCAL`] flag.
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/// Prefers picking a memory type with the [`DEVICE_LOCAL`] flag. **It does not affect whether
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/// the memory is host-visible**. You need to combine this with either the
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/// [`HOST_SEQUENTIAL_WRITE`] or [`HOST_RANDOM_ACCESS`] filter for that.
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///
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/// Memory being device-local means that it is fastest to access for the device. However,
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/// for dedicated GPUs, getting memory in and out of VRAM requires to go through the PCIe bus,
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@ -514,22 +524,22 @@ impl MemoryTypeFilter {
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/// memory types that are not `HOST_VISIBLE`, which makes sense since it's all system RAM. In
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/// that case you wouldn't need to do staging.
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///
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/// Don't use this together with [`PREFER_HOST`], that makes no sense. If you need host access,
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/// make sure you combine this with either the [`HOST_SEQUENTIAL_WRITE`] or
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/// [`HOST_RANDOM_ACCESS`] filter.
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/// Don't use this together with [`PREFER_HOST`], that makes no sense.
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///
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/// [`DEVICE_LOCAL`]: MemoryPropertyFlags::DEVICE_LOCAL
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/// [`HOST_VISIBLE`]: MemoryPropertyFlags::HOST_VISIBLE
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/// [`PREFER_HOST`]: Self::PREFER_HOST
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/// [`HOST_SEQUENTIAL_WRITE`]: Self::HOST_SEQUENTIAL_WRITE
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/// [`HOST_RANDOM_ACCESS`]: Self::HOST_RANDOM_ACCESS
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/// [`HOST_VISIBLE`]: MemoryPropertyFlags::HOST_VISIBLE
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/// [`PREFER_HOST`]: Self::PREFER_HOST
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pub const PREFER_DEVICE: Self = Self {
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required_flags: MemoryPropertyFlags::empty(),
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preferred_flags: MemoryPropertyFlags::DEVICE_LOCAL,
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not_preferred_flags: MemoryPropertyFlags::empty(),
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};
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/// Prefers picking a memory type without the [`DEVICE_LOCAL`] flag.
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/// Prefers picking a memory type without the [`DEVICE_LOCAL`] flag. **It does not affect
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/// whether the memory is host-visible**. You need to combine this with either the
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/// [`HOST_SEQUENTIAL_WRITE`] or [`HOST_RANDOM_ACCESS`] filter for that.
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///
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/// This option is best suited for resources that the host does access, but device doesn't
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/// access directly, such as staging buffers and readback buffers.
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@ -544,28 +554,29 @@ impl MemoryTypeFilter {
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/// still prefer host-local memory if the memory is rarely used, such as for manually paging
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/// parts of device-local memory out in order to free up space on the device.
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///
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/// Don't use this together with [`PREFER_DEVICE`], that makes no sense. If you need host
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/// access, make sure you combine this with either the [`HOST_SEQUENTIAL_WRITE`] or
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/// [`HOST_RANDOM_ACCESS`] filter.
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/// Don't use this together with [`PREFER_DEVICE`], that makes no sense.
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///
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/// [`DEVICE_LOCAL`]: MemoryPropertyFlags::DEVICE_LOCAL
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/// [`PREFER_DEVICE`]: Self::PREFER_DEVICE
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/// [`HOST_SEQUENTIAL_WRITE`]: Self::HOST_SEQUENTIAL_WRITE
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/// [`HOST_RANDOM_ACCESS`]: Self::HOST_RANDOM_ACCESS
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/// [`PREFER_DEVICE`]: Self::PREFER_DEVICE
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pub const PREFER_HOST: Self = Self {
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required_flags: MemoryPropertyFlags::empty(),
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preferred_flags: MemoryPropertyFlags::empty(),
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not_preferred_flags: MemoryPropertyFlags::DEVICE_LOCAL,
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};
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/// This guarantees picking a memory type that has the [`HOST_VISIBLE`] flag. Using this filter
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/// allows the allocator to pick a memory type that is uncached and write-combined, which is
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/// ideal for sequential writes. However, this optimization might lead to poor performance for
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/// anything else. What counts as a sequential write is any kind of loop that writes memory
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/// locations in order, such as iterating over a slice while writing each element in order, or
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/// equivalently using [`slice::copy_from_slice`]. Copying sized data also counts, as rustc
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/// should write the memory locations in order. If you have a struct, make sure you write it
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/// member-by-member.
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/// This guarantees picking a memory type that has the [`HOST_VISIBLE`] flag. **It does not
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/// affect whether the memory is device-local or host-local**. You need to combine this with
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/// either the [`PREFER_DEVICE`] or [`PREFER_HOST`] filter for that.
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///
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/// Using this filter allows the allocator to pick a memory type that is uncached and
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/// write-combined, which is ideal for sequential writes. However, this optimization might lead
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/// to poor performance for anything else. What counts as a sequential write is any kind of
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/// loop that writes memory locations in order, such as iterating over a slice while writing
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/// each element in order, or equivalently using [`slice::copy_from_slice`]. Copying sized data
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/// also counts, as rustc should write the memory locations in order. If you have a struct,
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/// make sure you write it member-by-member.
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///
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/// Example use cases include staging buffers, as well as any other kind of buffer that you
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/// only write to from the host, like a uniform or vertex buffer.
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@ -576,7 +587,8 @@ impl MemoryTypeFilter {
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/// to get the most performance out, if that's possible.
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///
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/// [`HOST_VISIBLE`]: MemoryPropertyFlags::HOST_VISIBLE
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/// [`HOST_COHERENT`]: MemoryPropertyFlags::HOST_COHERENT
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/// [`PREFER_DEVICE`]: Self::PREFER_DEVICE
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/// [`PREFER_HOST`]: Self::PREFER_HOST
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/// [`HOST_RANDOM_ACCESS`]: Self::HOST_RANDOM_ACCESS
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pub const HOST_SEQUENTIAL_WRITE: Self = Self {
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required_flags: MemoryPropertyFlags::HOST_VISIBLE,
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@ -585,7 +597,9 @@ impl MemoryTypeFilter {
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};
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/// This guarantees picking a memory type that has the [`HOST_VISIBLE`] and [`HOST_CACHED`]
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/// flags, which is best suited for readback and/or random access.
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/// flags, which is best suited for readback and/or random access. **It does not affect whether
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/// the memory is device-local or host-local**. You need to combine this with either the
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/// [`PREFER_DEVICE`] or [`PREFER_HOST`] filter for that.
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///
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/// Example use cases include using the device for things other than rendering and getting the
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/// results back to the host. That might be compute shading, or image or video manipulation, or
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@ -597,6 +611,8 @@ impl MemoryTypeFilter {
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///
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/// [`HOST_VISIBLE`]: MemoryPropertyFlags::HOST_VISIBLE
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/// [`HOST_CACHED`]: MemoryPropertyFlags::HOST_CACHED
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/// [`PREFER_DEVICE`]: Self::PREFER_DEVICE
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/// [`PREFER_HOST`]: Self::PREFER_HOST
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/// [`HOST_SEQUENTIAL_WRITE`]: Self::HOST_SEQUENTIAL_WRITE
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pub const HOST_RANDOM_ACCESS: Self = Self {
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required_flags: MemoryPropertyFlags::HOST_VISIBLE.union(MemoryPropertyFlags::HOST_CACHED),
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