Re: [RFC PATCH 00/18] TTM interface for managing VRAM oversubscription
Hi, On 02.05.24 16:23, Maarten Lankhorst wrote: Hey, [snip] For Xe, I've been loking at using cgroups. A small prototype is available at https://cgit.freedesktop.org/~mlankhorst/linux/log/?h=dumpcg To stimulate discussion, I've added amdgpu support as well. This should make it possible to isolate the compositor allocations from the target program. This support is still incomplete and covers vram only, but I need help from userspace and consensus from other drivers on how to move forward. I'm thinking of making 3 cgroup limits: 1. Physical memory, each time a buffer is allocated, it counts towards it, regardless where it resides. 2. Mappable memory, all buffers allocated in sysmem or vram count towards this limit. 3. VRAM, only buffers residing in VRAM count here. This ensures that VRAM can always be evicted to sysmem, by having a mappable memory quota, and having a sysmem reservation. The main trouble is that when evicting, you want to charge the original process the changes in allocation limits, but it should be solvable. I've been looking for someone else needing the usecase in a different context, so let me know what you think of the idea. Sorry for the late reply. The idea sounds really good! I think cgroups are great fit for what we'd need to prioritize game+compositor over other potential non-foreground apps. From what I can tell looking through the code, the current cgroup properties are absolute memory sizes that userspace asks the kernel to restrict the cgroup usage to? While that sounds useful for some usecases too, I'm not sure just these limits are a good solution for making sure that your compositor's and foreground app's resources stay in memory (in favor of background apps) when there is pressure. This can be generalized towards all uses of the GPU, but the compositor vs game thrashing is a good example of why it is useful to have. IIRC Tvrtko's original proposal was about per-cgroup DRM scheduling priorities providing lower submission latency for prioritized cgroups, right? I think what we need here would pretty much exactly such a priority system, but for memory: The cgroup containing the foreground app/game and the compositor should have some hint telling TTM to try its hardest to avoid evicting its buffers (i.e. a high memory priority). Your existing drm_cgroup work looks like a great base for this, and I'd be happy to help/participate with the implementation for amdgpu. Thanks, Friedrich I should still have my cgroup testcase somewhere, this is only a rebase of my previous proposal, but I think it fits the usecase. Cheers, Maarten
Re: [RFC PATCH 00/18] TTM interface for managing VRAM oversubscription
Hey, Den 2024-04-24 kl. 18:56, skrev Friedrich Vock: Hi everyone, recently I've been looking into remedies for apps (in particular, newer games) that experience significant performance loss when they start to hit VRAM limits, especially on older or lower-end cards that struggle to fit both desktop apps and all the game data into VRAM at once. The root of the problem lies in the fact that from userspace's POV, buffer eviction is very opaque: Userspace applications/drivers cannot tell how oversubscribed VRAM is, nor do they have fine-grained control over which buffers get evicted. At the same time, with GPU APIs becoming increasingly lower-level and GPU-driven, only the application itself can know which buffers are used within a particular submission, and how important each buffer is. For this, GPU APIs include interfaces to query oversubscription and specify memory priorities: In Vulkan, oversubscription can be queried through the VK_EXT_memory_budget extension. Different buffers can also be assigned priorities via the VK_EXT_pageable_device_local_memory extension. Modern games, especially D3D12 games via vkd3d-proton, rely on oversubscription being reported and priorities being respected in order to perform their memory management. However, relaying this information to the kernel via the current KMD uAPIs is not possible. On AMDGPU for example, all work submissions include a "bo list" that contains any buffer object that is accessed during the course of the submission. If VRAM is oversubscribed and a buffer in the list was evicted to system memory, that buffer is moved back to VRAM (potentially evicting other unused buffers). Since the usermode driver doesn't know what buffers are used by the application, its only choice is to submit a bo list that contains every buffer the application has allocated. In case of VRAM oversubscription, it is highly likely that some of the application's buffers were evicted, which almost guarantees that some buffers will get moved around. Since the bo list is only known at submit time, this also means the buffers will get moved right before submitting application work, which is the worst possible time to move buffers from a latency perspective. Another consequence of the large bo list is that nearly all memory from other applications will be evicted, too. When different applications (e.g. game and compositor) submit work one after the other, this causes a ping-pong effect where each app's submission evicts the other app's memory, resulting in a large amount of unnecessary moves. This overly aggressive eviction behavior led to RADV adopting a change that effectively allows all VRAM applications to reside in system memory [1]. This worked around the ping-ponging/excessive buffer moving problem, but also meant that any memory evicted to system memory would forever stay there, regardless of how VRAM is used. My proposal aims at providing a middle ground between these extremes. The goals I want to meet are: - Userspace is accurately informed about VRAM oversubscription/how much VRAM has been evicted - Buffer eviction respects priorities set by userspace - Wasteful ping-ponging is avoided to the extent possible I have been testing out some prototypes, and came up with this rough sketch of an API: - For each ttm_resource_manager, the amount of evicted memory is tracked (similarly to how "usage" tracks the memory usage). When memory is evicted via ttm_bo_evict, the size of the evicted memory is added, when memory is un-evicted (see below), its size is subtracted. The amount of evicted memory for e.g. VRAM can be queried by userspace via an ioctl. - Each ttm_resource_manager maintains a list of evicted buffer objects. - ttm_mem_unevict walks the list of evicted bos for a given ttm_resource_manager and tries moving evicted resources back. When a buffer is freed, this function is called to immediately restore some evicted memory. - Each ttm_buffer_object independently tracks the mem_type it wants to reside in. - ttm_bo_try_unevict is added as a helper function which attempts to move the buffer to its preferred mem_type. If no space is available there, it fails with -ENOSPC/-ENOMEM. - Similar to how ttm_bo_evict works, each driver can implement uneviction_valuable/unevict_flags callbacks to control buffer un-eviction. This is what patches 1-10 accomplish (together with an amdgpu implementation utilizing the new API). Userspace priorities could then be implemented as follows: - TTM already manages priorities for each buffer object. These priorities can be updated by userspace via a GEM_OP ioctl to inform the kernel which buffers should be evicted before others. If an ioctl increases the priority of a buffer, ttm_bo_try_unevict is called on that buffer to try and move it back (potentially evicting buffers with a lower priority) - Buffers should never be evicted by other buffers with equal/lower priority, but
Re: [RFC PATCH 00/18] TTM interface for managing VRAM oversubscription
Yeah, and this patch set here is removing that functionality. Which is major concern from my side as well. Instead of removing it my long term plan was to move this into TTM ( the recent flags rework is going into that direction), so that both amdgpu and radeon can use the same code again *and* we can also apply it on VM_ALWAYS_VALID BOs. Christian. Am 25.04.24 um 15:22 schrieb Marek Olšák: The most extreme ping-ponging is mitigated by throttling buffer moves in the kernel, but it only works without VM_ALWAYS_VALID and you can set BO priorities in the BO list. A better approach that works with VM_ALWAYS_VALID would be nice. Marek On Wed, Apr 24, 2024 at 1:12 PM Friedrich Vock wrote: Hi everyone, recently I've been looking into remedies for apps (in particular, newer games) that experience significant performance loss when they start to hit VRAM limits, especially on older or lower-end cards that struggle to fit both desktop apps and all the game data into VRAM at once. The root of the problem lies in the fact that from userspace's POV, buffer eviction is very opaque: Userspace applications/drivers cannot tell how oversubscribed VRAM is, nor do they have fine-grained control over which buffers get evicted. At the same time, with GPU APIs becoming increasingly lower-level and GPU-driven, only the application itself can know which buffers are used within a particular submission, and how important each buffer is. For this, GPU APIs include interfaces to query oversubscription and specify memory priorities: In Vulkan, oversubscription can be queried through the VK_EXT_memory_budget extension. Different buffers can also be assigned priorities via the VK_EXT_pageable_device_local_memory extension. Modern games, especially D3D12 games via vkd3d-proton, rely on oversubscription being reported and priorities being respected in order to perform their memory management. However, relaying this information to the kernel via the current KMD uAPIs is not possible. On AMDGPU for example, all work submissions include a "bo list" that contains any buffer object that is accessed during the course of the submission. If VRAM is oversubscribed and a buffer in the list was evicted to system memory, that buffer is moved back to VRAM (potentially evicting other unused buffers). Since the usermode driver doesn't know what buffers are used by the application, its only choice is to submit a bo list that contains every buffer the application has allocated. In case of VRAM oversubscription, it is highly likely that some of the application's buffers were evicted, which almost guarantees that some buffers will get moved around. Since the bo list is only known at submit time, this also means the buffers will get moved right before submitting application work, which is the worst possible time to move buffers from a latency perspective. Another consequence of the large bo list is that nearly all memory from other applications will be evicted, too. When different applications (e.g. game and compositor) submit work one after the other, this causes a ping-pong effect where each app's submission evicts the other app's memory, resulting in a large amount of unnecessary moves. This overly aggressive eviction behavior led to RADV adopting a change that effectively allows all VRAM applications to reside in system memory [1]. This worked around the ping-ponging/excessive buffer moving problem, but also meant that any memory evicted to system memory would forever stay there, regardless of how VRAM is used. My proposal aims at providing a middle ground between these extremes. The goals I want to meet are: - Userspace is accurately informed about VRAM oversubscription/how much VRAM has been evicted - Buffer eviction respects priorities set by userspace - Wasteful ping-ponging is avoided to the extent possible I have been testing out some prototypes, and came up with this rough sketch of an API: - For each ttm_resource_manager, the amount of evicted memory is tracked (similarly to how "usage" tracks the memory usage). When memory is evicted via ttm_bo_evict, the size of the evicted memory is added, when memory is un-evicted (see below), its size is subtracted. The amount of evicted memory for e.g. VRAM can be queried by userspace via an ioctl. - Each ttm_resource_manager maintains a list of evicted buffer objects. - ttm_mem_unevict walks the list of evicted bos for a given ttm_resource_manager and tries moving evicted resources back. When a buffer is freed, this function is called to immediately restore some evicted memory. - Each ttm_buffer_object independently tracks the mem_type it wants to reside in. - ttm_bo_try_unevict is added as a helper function which attempts to move the buffer to its preferred mem_type. If no space is available there, it fails with -ENOSPC/-ENOMEM. - Similar to how ttm_bo_evict works, each driver can implement uneviction_valuable/unevict_flags callbacks to
Re: [RFC PATCH 00/18] TTM interface for managing VRAM oversubscription
The most extreme ping-ponging is mitigated by throttling buffer moves in the kernel, but it only works without VM_ALWAYS_VALID and you can set BO priorities in the BO list. A better approach that works with VM_ALWAYS_VALID would be nice. Marek On Wed, Apr 24, 2024 at 1:12 PM Friedrich Vock wrote: > > Hi everyone, > > recently I've been looking into remedies for apps (in particular, newer > games) that experience significant performance loss when they start to > hit VRAM limits, especially on older or lower-end cards that struggle > to fit both desktop apps and all the game data into VRAM at once. > > The root of the problem lies in the fact that from userspace's POV, > buffer eviction is very opaque: Userspace applications/drivers cannot > tell how oversubscribed VRAM is, nor do they have fine-grained control > over which buffers get evicted. At the same time, with GPU APIs becoming > increasingly lower-level and GPU-driven, only the application itself > can know which buffers are used within a particular submission, and > how important each buffer is. For this, GPU APIs include interfaces > to query oversubscription and specify memory priorities: In Vulkan, > oversubscription can be queried through the VK_EXT_memory_budget > extension. Different buffers can also be assigned priorities via the > VK_EXT_pageable_device_local_memory extension. Modern games, especially > D3D12 games via vkd3d-proton, rely on oversubscription being reported and > priorities being respected in order to perform their memory management. > > However, relaying this information to the kernel via the current KMD uAPIs > is not possible. On AMDGPU for example, all work submissions include a > "bo list" that contains any buffer object that is accessed during the > course of the submission. If VRAM is oversubscribed and a buffer in the > list was evicted to system memory, that buffer is moved back to VRAM > (potentially evicting other unused buffers). > > Since the usermode driver doesn't know what buffers are used by the > application, its only choice is to submit a bo list that contains every > buffer the application has allocated. In case of VRAM oversubscription, > it is highly likely that some of the application's buffers were evicted, > which almost guarantees that some buffers will get moved around. Since > the bo list is only known at submit time, this also means the buffers > will get moved right before submitting application work, which is the > worst possible time to move buffers from a latency perspective. Another > consequence of the large bo list is that nearly all memory from other > applications will be evicted, too. When different applications (e.g. game > and compositor) submit work one after the other, this causes a ping-pong > effect where each app's submission evicts the other app's memory, > resulting in a large amount of unnecessary moves. > > This overly aggressive eviction behavior led to RADV adopting a change > that effectively allows all VRAM applications to reside in system memory > [1]. This worked around the ping-ponging/excessive buffer moving problem, > but also meant that any memory evicted to system memory would forever > stay there, regardless of how VRAM is used. > > My proposal aims at providing a middle ground between these extremes. > The goals I want to meet are: > - Userspace is accurately informed about VRAM oversubscription/how much > VRAM has been evicted > - Buffer eviction respects priorities set by userspace - Wasteful > ping-ponging is avoided to the extent possible > > I have been testing out some prototypes, and came up with this rough > sketch of an API: > > - For each ttm_resource_manager, the amount of evicted memory is tracked > (similarly to how "usage" tracks the memory usage). When memory is > evicted via ttm_bo_evict, the size of the evicted memory is added, when > memory is un-evicted (see below), its size is subtracted. The amount of > evicted memory for e.g. VRAM can be queried by userspace via an ioctl. > > - Each ttm_resource_manager maintains a list of evicted buffer objects. > > - ttm_mem_unevict walks the list of evicted bos for a given > ttm_resource_manager and tries moving evicted resources back. When a > buffer is freed, this function is called to immediately restore some > evicted memory. > > - Each ttm_buffer_object independently tracks the mem_type it wants > to reside in. > > - ttm_bo_try_unevict is added as a helper function which attempts to > move the buffer to its preferred mem_type. If no space is available > there, it fails with -ENOSPC/-ENOMEM. > > - Similar to how ttm_bo_evict works, each driver can implement > uneviction_valuable/unevict_flags callbacks to control buffer > un-eviction. > > This is what patches 1-10 accomplish (together with an amdgpu > implementation utilizing the new API). > > Userspace priorities could then be implemented as follows: > > - TTM already manages priorities for each buffer object. These
Re: [RFC PATCH 00/18] TTM interface for managing VRAM oversubscription
In general: Yes please :) But are exercising a lot of ideas we have already thrown over board over the years. The general idea Marek and I have been working on for a while now is rather to make TTM aware of userspace "clients". In other words we should start with having a TTM structure in the fpriv of the drivers and then track there how much VRAM was evicted for each client. This should then be balanced so that each client gets it's equal share of VRAM and we pretty much end up with a static situation which only changes when applications become inactive/active (based on their GPU activity). I will mail you some of the stuff we already came up with later on. Regards, Christian. Am 24.04.24 um 18:56 schrieb Friedrich Vock: Hi everyone, recently I've been looking into remedies for apps (in particular, newer games) that experience significant performance loss when they start to hit VRAM limits, especially on older or lower-end cards that struggle to fit both desktop apps and all the game data into VRAM at once. The root of the problem lies in the fact that from userspace's POV, buffer eviction is very opaque: Userspace applications/drivers cannot tell how oversubscribed VRAM is, nor do they have fine-grained control over which buffers get evicted. At the same time, with GPU APIs becoming increasingly lower-level and GPU-driven, only the application itself can know which buffers are used within a particular submission, and how important each buffer is. For this, GPU APIs include interfaces to query oversubscription and specify memory priorities: In Vulkan, oversubscription can be queried through the VK_EXT_memory_budget extension. Different buffers can also be assigned priorities via the VK_EXT_pageable_device_local_memory extension. Modern games, especially D3D12 games via vkd3d-proton, rely on oversubscription being reported and priorities being respected in order to perform their memory management. However, relaying this information to the kernel via the current KMD uAPIs is not possible. On AMDGPU for example, all work submissions include a "bo list" that contains any buffer object that is accessed during the course of the submission. If VRAM is oversubscribed and a buffer in the list was evicted to system memory, that buffer is moved back to VRAM (potentially evicting other unused buffers). Since the usermode driver doesn't know what buffers are used by the application, its only choice is to submit a bo list that contains every buffer the application has allocated. In case of VRAM oversubscription, it is highly likely that some of the application's buffers were evicted, which almost guarantees that some buffers will get moved around. Since the bo list is only known at submit time, this also means the buffers will get moved right before submitting application work, which is the worst possible time to move buffers from a latency perspective. Another consequence of the large bo list is that nearly all memory from other applications will be evicted, too. When different applications (e.g. game and compositor) submit work one after the other, this causes a ping-pong effect where each app's submission evicts the other app's memory, resulting in a large amount of unnecessary moves. This overly aggressive eviction behavior led to RADV adopting a change that effectively allows all VRAM applications to reside in system memory [1]. This worked around the ping-ponging/excessive buffer moving problem, but also meant that any memory evicted to system memory would forever stay there, regardless of how VRAM is used. My proposal aims at providing a middle ground between these extremes. The goals I want to meet are: - Userspace is accurately informed about VRAM oversubscription/how much VRAM has been evicted - Buffer eviction respects priorities set by userspace - Wasteful ping-ponging is avoided to the extent possible I have been testing out some prototypes, and came up with this rough sketch of an API: - For each ttm_resource_manager, the amount of evicted memory is tracked (similarly to how "usage" tracks the memory usage). When memory is evicted via ttm_bo_evict, the size of the evicted memory is added, when memory is un-evicted (see below), its size is subtracted. The amount of evicted memory for e.g. VRAM can be queried by userspace via an ioctl. - Each ttm_resource_manager maintains a list of evicted buffer objects. - ttm_mem_unevict walks the list of evicted bos for a given ttm_resource_manager and tries moving evicted resources back. When a buffer is freed, this function is called to immediately restore some evicted memory. - Each ttm_buffer_object independently tracks the mem_type it wants to reside in. - ttm_bo_try_unevict is added as a helper function which attempts to move the buffer to its preferred mem_type. If no space is available there, it fails with -ENOSPC/-ENOMEM. - Similar to how ttm_bo_evict works, each driver can implement
[RFC PATCH 00/18] TTM interface for managing VRAM oversubscription
Hi everyone, recently I've been looking into remedies for apps (in particular, newer games) that experience significant performance loss when they start to hit VRAM limits, especially on older or lower-end cards that struggle to fit both desktop apps and all the game data into VRAM at once. The root of the problem lies in the fact that from userspace's POV, buffer eviction is very opaque: Userspace applications/drivers cannot tell how oversubscribed VRAM is, nor do they have fine-grained control over which buffers get evicted. At the same time, with GPU APIs becoming increasingly lower-level and GPU-driven, only the application itself can know which buffers are used within a particular submission, and how important each buffer is. For this, GPU APIs include interfaces to query oversubscription and specify memory priorities: In Vulkan, oversubscription can be queried through the VK_EXT_memory_budget extension. Different buffers can also be assigned priorities via the VK_EXT_pageable_device_local_memory extension. Modern games, especially D3D12 games via vkd3d-proton, rely on oversubscription being reported and priorities being respected in order to perform their memory management. However, relaying this information to the kernel via the current KMD uAPIs is not possible. On AMDGPU for example, all work submissions include a "bo list" that contains any buffer object that is accessed during the course of the submission. If VRAM is oversubscribed and a buffer in the list was evicted to system memory, that buffer is moved back to VRAM (potentially evicting other unused buffers). Since the usermode driver doesn't know what buffers are used by the application, its only choice is to submit a bo list that contains every buffer the application has allocated. In case of VRAM oversubscription, it is highly likely that some of the application's buffers were evicted, which almost guarantees that some buffers will get moved around. Since the bo list is only known at submit time, this also means the buffers will get moved right before submitting application work, which is the worst possible time to move buffers from a latency perspective. Another consequence of the large bo list is that nearly all memory from other applications will be evicted, too. When different applications (e.g. game and compositor) submit work one after the other, this causes a ping-pong effect where each app's submission evicts the other app's memory, resulting in a large amount of unnecessary moves. This overly aggressive eviction behavior led to RADV adopting a change that effectively allows all VRAM applications to reside in system memory [1]. This worked around the ping-ponging/excessive buffer moving problem, but also meant that any memory evicted to system memory would forever stay there, regardless of how VRAM is used. My proposal aims at providing a middle ground between these extremes. The goals I want to meet are: - Userspace is accurately informed about VRAM oversubscription/how much VRAM has been evicted - Buffer eviction respects priorities set by userspace - Wasteful ping-ponging is avoided to the extent possible I have been testing out some prototypes, and came up with this rough sketch of an API: - For each ttm_resource_manager, the amount of evicted memory is tracked (similarly to how "usage" tracks the memory usage). When memory is evicted via ttm_bo_evict, the size of the evicted memory is added, when memory is un-evicted (see below), its size is subtracted. The amount of evicted memory for e.g. VRAM can be queried by userspace via an ioctl. - Each ttm_resource_manager maintains a list of evicted buffer objects. - ttm_mem_unevict walks the list of evicted bos for a given ttm_resource_manager and tries moving evicted resources back. When a buffer is freed, this function is called to immediately restore some evicted memory. - Each ttm_buffer_object independently tracks the mem_type it wants to reside in. - ttm_bo_try_unevict is added as a helper function which attempts to move the buffer to its preferred mem_type. If no space is available there, it fails with -ENOSPC/-ENOMEM. - Similar to how ttm_bo_evict works, each driver can implement uneviction_valuable/unevict_flags callbacks to control buffer un-eviction. This is what patches 1-10 accomplish (together with an amdgpu implementation utilizing the new API). Userspace priorities could then be implemented as follows: - TTM already manages priorities for each buffer object. These priorities can be updated by userspace via a GEM_OP ioctl to inform the kernel which buffers should be evicted before others. If an ioctl increases the priority of a buffer, ttm_bo_try_unevict is called on that buffer to try and move it back (potentially evicting buffers with a lower priority) - Buffers should never be evicted by other buffers with equal/lower priority, but if there is a buffer with lower priority occupying VRAM, it should be
