By the way, are you using all-open driver or amdgpu-pro driver?
+David Mao, who is working on our Vulkan driver.
Regards,
David Zhou
On 2016å¹´12æ??18æ?¥ 06:05, Pierre-Loup A. Griffais wrote:
> Hi Serguei,
>
> I'm also working on the bringing up our VR runtime on top of amgpu;
> see replies inline.
>
> On 12/16/2016 09:05 PM, Sagalovitch, Serguei wrote:
>> Andres,
>>
>>> For current VR workloads we have 3 separate processes running
>>> actually:
>> So we could have potential memory overcommit case or do you do
>> partitioning
>> on your own? I would think that there is need to avoid overcomit in
>> VR case to
>> prevent any BO migration.
>
> You're entirely correct; currently the VR runtime is setting up
> prioritized CPU scheduling for its VR compositor, we're working on
> prioritized GPU scheduling and pre-emption (eg. this thread), and in
> the future it will make sense to do work in order to make sure that
> its memory allocations do not get evicted, to prevent any unwelcome
> additional latency in the event of needing to perform just-in-time
> reprojection.
>
>> BTW: Do you mean __real__ processes or threads?
>> Based on my understanding sharing BOs between different processes
>> could introduce additional synchronization constrains. btw: I am not
>> sure
>> if we are able to share Vulkan sync. object cross-process boundary.
>
> They are different processes; it is important for the compositor that
> is responsible for quality-of-service features such as consistently
> presenting distorted frames with the right latency, reprojection, etc,
> to be separate from the main application.
>
> Currently we are using unreleased cross-process memory and semaphore
> extensions to fetch updated eye images from the client application,
> but the just-in-time reprojection discussed here does not actually
> have any direct interactions with cross-process resource sharing,
> since it's achieved by using whatever is the latest, most up-to-date
> eye images that have already been sent by the client application,
> which are already available to use without additional synchronization.
>
>>
>>> 3) System compositor (we are looking at approaches to remove this
>>> overhead)
>> Yes, IMHO the best is to run in "full screen mode".
>
> Yes, we are working on mechanisms to present directly to the headset
> display without any intermediaries as a separate effort.
>
>>
>>> The latency is our main concern,
>> I would assume that this is the known problem (at least for compute
>> usage).
>> It looks like that amdgpu / kernel submission is rather CPU intensive
>> (at least
>> in the default configuration).
>
> As long as it's a consistent cost, it shouldn't an issue. However, if
> there's high degrees of variance then that would be troublesome and we
> would need to account for the worst case.
>
> Hopefully the requirements and approach we described make sense, we're
> looking forward to your feedback and suggestions.
>
> Thanks!
> - Pierre-Loup
>
>>
>> Sincerely yours,
>> Serguei Sagalovitch
>>
>>
>> From: Andres Rodriguez <andresr at valvesoftware.com>
>> Sent: December 16, 2016 10:00 PM
>> To: Sagalovitch, Serguei; amd-gfx at lists.freedesktop.org
>> Subject: RE: [RFC] Mechanism for high priority scheduling in amdgpu
>>
>> Hey Serguei,
>>
>>> [Serguei] No. I mean pipe :-) as MEC define it. As far as I
>>> understand (by simplifying)
>>> some scheduling is per pipe. I know about the current allocation
>>> scheme but I do not think
>>> that it is ideal. I would assume that we need to switch to
>>> dynamical partition
>>> of resources based on the workload otherwise we will have resource
>>> conflict
>>> between Vulkan compute and OpenCL.
>>
>> I agree the partitioning isn't ideal. I'm hoping we can start with a
>> solution that assumes that
>> only pipe0 has any work and the other pipes are idle (no HSA/ROCm
>> running on the system).
>>
>> This should be more or less the use case we expect from VR users.
>>
>> I agree the split is currently not ideal, but I'd like to consider
>> that a separate task, because
>> making it dynamic is not straight forward :P
>>
>>> [Serguei] Vulkan works via amdgpu (kernel submissions) so amdkfd
>>> will be not
>>> involved. I would assume that in the case of VR we will have one main
>>> application ("console" mode(?)) so we could temporally "ignore"
>>> OpenCL/ROCm needs when VR is running.
>>
>> Correct, this is why we want to enable the high priority compute
>> queue through
>> libdrm-amdgpu, so that we can expose it through Vulkan later.
>>
>> For current VR workloads we have 3 separate processes running actually:
>> 1) Game process
>> 2) VR Compositor (this is the process that will require high
>> priority queue)
>> 3) System compositor (we are looking at approaches to remove this
>> overhead)
>>
>> For now I think it is okay to assume no OpenCL/ROCm running
>> simultaneously, but
>> I would also like to be able to address this case in the future
>> (cross-pipe priorities).
>>
>>> [Serguei] The problem with pre-emption of graphics task: (a) it
>>> may take time so
>>> latency may suffer
>>
>> The latency is our main concern, we want something that is
>> predictable. A good
>> illustration of what the reprojection scheduling looks like can be
>> found here:
>> https://community.amd.com/servlet/JiveServlet/showImage/38-1310-104754/pastedImage_3.png
>>
>>
>>> (b) to preempt we need to have different "context" - we want
>>> to guarantee that submissions from the same context will be executed
>>> in order.
>>
>> This is okay, as the reprojection work doesn't have dependencies on
>> the game context, and it
>> even happens in a separate process.
>>
>>> BTW: (a) Do you want "preempt" and later resume or do you want
>>> "preempt" and
>>> "cancel/abort"
>>
>> Preempt the game with the compositor task and then resume it.
>>
>>> (b) Vulkan is generic API and could be used for graphics as well as
>>> for plain compute tasks (VK_QUEUE_COMPUTE_BIT).
>>
>> Yeah, the plan is to use vulkan compute. But if you figure out a way
>> for us to get
>> a guaranteed execution time using vulkan graphics, then I'll take you
>> out for a beer :)
>>
>> Regards,
>> Andres
>> ________________________________________
>> From: Sagalovitch, Serguei [Serguei.Sagalovitch at amd.com]
>> Sent: Friday, December 16, 2016 9:13 PM
>> To: Andres Rodriguez; amd-gfx at lists.freedesktop.org
>> Subject: Re: [RFC] Mechanism for high priority scheduling in amdgpu
>>
>> Hi Andres,
>>
>> Please see inline (as [Serguei])
>>
>> Sincerely yours,
>> Serguei Sagalovitch
>>
>>
>> From: Andres Rodriguez <andresr at valvesoftware.com>
>> Sent: December 16, 2016 8:29 PM
>> To: Sagalovitch, Serguei; amd-gfx at lists.freedesktop.org
>> Subject: RE: [RFC] Mechanism for high priority scheduling in amdgpu
>>
>> Hi Serguei,
>>
>> Thanks for the feedback. Answers inline as [AR].
>>
>> Regards,
>> Andres
>>
>> ________________________________________
>> From: Sagalovitch, Serguei [Serguei.Sagalovitch at amd.com]
>> Sent: Friday, December 16, 2016 8:15 PM
>> To: Andres Rodriguez; amd-gfx at lists.freedesktop.org
>> Subject: Re: [RFC] Mechanism for high priority scheduling in amdgpu
>>
>> Andres,
>>
>>
>> Quick comments:
>>
>> 1) To minimize "bubbles", etc. we need to "force" CU assignments/binding
>> to high-priority queue when it will be in use and "free" them later
>> (we do not want forever take CUs from e.g. graphic task to degrade
>> graphics
>> performance).
>>
>> Otherwise we could have scenario when long graphics task (or
>> low-priority
>> compute) will took all (extra) CUs and high--priority will wait for
>> needed resources.
>> It will not be visible on "NOP " but only when you submit "real"
>> compute task
>> so I would recommend not to use "NOP" packets at all for testing.
>>
>> It (CU assignment) could be relatively easy done when everything is
>> going via kernel
>> (e.g. as part of frame submission) but I must admit that I am not sure
>> about the best way for user level submissions (amdkfd).
>>
>> [AR] I wasn't aware of this part of the programming sequence. Thanks
>> for the heads up!
>> Is this similar to the CU masking programming?
>> [Serguei] Yes. To simplify: the problem is that "scheduler" when
>> deciding which
>> queue to run will check if there is enough resources and if not then
>> it will begin
>> to check other queues with lower priority.
>>
>> 2) I would recommend to dedicate the whole pipe to high-priority
>> queue and have
>> nothing their except it.
>>
>> [AR] I'm guessing in this context you mean pipe = queue? (as opposed
>> to the MEC definition
>> of pipe, which is a grouping of queues). I say this because amdgpu
>> only has access to 1 pipe,
>> and the rest are statically partitioned for amdkfd usage.
>>
>> [Serguei] No. I mean pipe :-) as MEC define it. As far as I
>> understand (by simplifying)
>> some scheduling is per pipe. I know about the current allocation
>> scheme but I do not think
>> that it is ideal. I would assume that we need to switch to
>> dynamical partition
>> of resources based on the workload otherwise we will have resource
>> conflict
>> between Vulkan compute and OpenCL.
>>
>>
>> BTW: Which user level API do you want to use for compute: Vulkan or
>> OpenCL?
>>
>> [AR] Vulkan
>>
>> [Serguei] Vulkan works via amdgpu (kernel submissions) so amdkfd will
>> be not
>> involved. I would assume that in the case of VR we will have one main
>> application ("console" mode(?)) so we could temporally "ignore"
>> OpenCL/ROCm needs when VR is running.
>>
>>> we will not be able to provide a solution compatible with GFX
>>> worloads.
>> I assume that you are talking about graphics? Am I right?
>>
>> [AR] Yeah, my understanding is that pre-empting the currently running
>> graphics job and scheduling in
>> something else using mid-buffer pre-emption has some cases where it
>> doesn't work well. But if with
>> polaris10 it starts working well, it might be a better solution for
>> us (because the whole reprojection
>> work uses the vulkan graphics stack at the moment, and porting it to
>> compute is not trivial).
>>
>> [Serguei] The problem with pre-emption of graphics task: (a) it may
>> take time so
>> latency may suffer (b) to preempt we need to have different "context"
>> - we want
>> to guarantee that submissions from the same context will be executed
>> in order.
>> BTW: (a) Do you want "preempt" and later resume or do you want
>> "preempt" and
>> "cancel/abort"? (b) Vulkan is generic API and could be used
>> for graphics as well as for plain compute tasks (VK_QUEUE_COMPUTE_BIT).
>>
>>
>> Sincerely yours,
>> Serguei Sagalovitch
>>
>>
>>
>> From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> on behalf of
>> Andres Rodriguez <andresr at valvesoftware.com>
>> Sent: December 16, 2016 6:15 PM
>> To: amd-gfx at lists.freedesktop.org
>> Subject: [RFC] Mechanism for high priority scheduling in amdgpu
>>
>> Hi Everyone,
>>
>> This RFC is also available as a gist here:
>> https://gist.github.com/lostgoat/7000432cd6864265dbc2c3ab93204249
>>
>>
>>
>> [RFC] Mechanism for high priority scheduling in amdgpu
>> gist.github.com
>> [RFC] Mechanism for high priority scheduling in amdgpu
>>
>>
>>
>> [RFC] Mechanism for high priority scheduling in amdgpu
>> gist.github.com
>> [RFC] Mechanism for high priority scheduling in amdgpu
>>
>>
>>
>>
>> [RFC] Mechanism for high priority scheduling in amdgpu
>> gist.github.com
>> [RFC] Mechanism for high priority scheduling in amdgpu
>>
>>
>> We are interested in feedback for a mechanism to effectively schedule
>> high
>> priority VR reprojection tasks (also referred to as time-warping) for
>> Polaris10
>> running on the amdgpu kernel driver.
>>
>> Brief context:
>> --------------
>>
>> The main objective of reprojection is to avoid motion sickness for VR
>> users in
>> scenarios where the game or application would fail to finish
>> rendering a new
>> frame in time for the next VBLANK. When this happens, the user's head
>> movements
>> are not reflected on the Head Mounted Display (HMD) for the duration
>> of an
>> extra frame. This extended mismatch between the inner ear and the
>> eyes may
>> cause the user to experience motion sickness.
>>
>> The VR compositor deals with this problem by fabricating a new frame
>> using the
>> user's updated head position in combination with the previous frames.
>> This
>> avoids a prolonged mismatch between the HMD output and the inner ear.
>>
>> Because of the adverse effects on the user, we require high
>> confidence that the
>> reprojection task will complete before the VBLANK interval. Even if
>> the GFX pipe
>> is currently full of work from the game/application (which is most
>> likely the case).
>>
>> For more details and illustrations, please refer to the following
>> document:
>> https://community.amd.com/community/gaming/blog/2016/03/28/asynchronous-shaders-evolved
>>
>>
>>
>> Gaming: Asynchronous Shaders Evolved | Community
>> community.amd.com
>> One of the most exciting new developments in GPU technology over the
>> past year has been the adoption of asynchronous shaders, which can
>> make more efficient use of ...
>>
>>
>>
>> Gaming: Asynchronous Shaders Evolved | Community
>> community.amd.com
>> One of the most exciting new developments in GPU technology over the
>> past year has been the adoption of asynchronous shaders, which can
>> make more efficient use of ...
>>
>>
>>
>> Gaming: Asynchronous Shaders Evolved | Community
>> community.amd.com
>> One of the most exciting new developments in GPU technology over the
>> past year has been the adoption of asynchronous shaders, which can
>> make more efficient use of ...
>>
>>
>> Requirements:
>> -------------
>>
>> The mechanism must expose the following functionaility:
>>
>> * Job round trip time must be predictable, from submission to
>> fence signal
>>
>> * The mechanism must support compute workloads.
>>
>> Goals:
>> ------
>>
>> * The mechanism should provide low submission latencies
>>
>> Test: submitting a NOP packet through the mechanism on busy hardware
>> should
>> be equivalent to submitting a NOP on idle hardware.
>>
>> Nice to have:
>> -------------
>>
>> * The mechanism should also support GFX workloads.
>>
>> My understanding is that with the current hardware capabilities in
>> Polaris10 we
>> will not be able to provide a solution compatible with GFX worloads.
>>
>> But I would love to hear otherwise. So if anyone has an idea,
>> approach or
>> suggestion that will also be compatible with the GFX ring, please let
>> us know
>> about it.
>>
>> * The above guarantees should also be respected by amdkfd workloads
>>
>> Would be good to have for consistency, but not strictly necessary as
>> users running
>> games are not traditionally running HPC workloads in the background.
>>
>> Proposed approach:
>> ------------------
>>
>> Similar to the windows driver, we could expose a high priority
>> compute queue to
>> userspace.
>>
>> Submissions to this compute queue will be scheduled with high
>> priority, and may
>> acquire hardware resources previously in use by other queues.
>>
>> This can be achieved by taking advantage of the 'priority' field in
>> the HQDs
>> and could be programmed by amdgpu or the amdgpu scheduler. The relevant
>> register fields are:
>> * mmCP_HQD_PIPE_PRIORITY
>> * mmCP_HQD_QUEUE_PRIORITY
>>
>> Implementation approach 1 - static partitioning:
>> ------------------------------------------------
>>
>> The amdgpu driver currently controls 8 compute queues from pipe0. We can
>> statically partition these as follows:
>> * 7x regular
>> * 1x high priority
>>
>> The relevant priorities can be set so that submissions to the high
>> priority
>> ring will starve the other compute rings and the GFX ring.
>>
>> The amdgpu scheduler will only place jobs into the high priority
>> rings if the
>> context is marked as high priority. And a corresponding priority
>> should be
>> added to keep track of this information:
>> * AMD_SCHED_PRIORITY_KERNEL
>> * -> AMD_SCHED_PRIORITY_HIGH
>> * AMD_SCHED_PRIORITY_NORMAL
>>
>> The user will request a high priority context by setting an
>> appropriate flag
>> in drm_amdgpu_ctx_in (AMDGPU_CTX_HIGH_PRIORITY or similar):
>> https://github.com/torvalds/linux/blob/master/include/uapi/drm/amdgpu_drm.h#L163
>>
>>
>> The setting is in a per context level so that we can:
>> * Maintain a consistent FIFO ordering of all submissions to a
>> context
>> * Create high priority and non-high priority contexts in the same
>> process
>>
>> Implementation approach 2 - dynamic priority programming:
>> ---------------------------------------------------------
>>
>> Similar to the above, but instead of programming the priorities and
>> amdgpu_init() time, the SW scheduler will reprogram the queue priorities
>> dynamically when scheduling a task.
>>
>> This would involve having a hardware specific callback from the
>> scheduler to
>> set the appropriate queue priority: set_priority(int ring, int index,
>> int priority)
>>
>> During this callback we would have to grab the SRBM mutex to perform
>> the appropriate
>> HW programming, and I'm not really sure if that is something we
>> should be doing from
>> the scheduler.
>>
>> On the positive side, this approach would allow us to program a range of
>> priorities for jobs instead of a single "high priority" value",
>> achieving
>> something similar to the niceness API available for CPU scheduling.
>>
>> I'm not sure if this flexibility is something that we would need for
>> our use
>> case, but it might be useful in other scenarios (multiple users
>> sharing compute
>> time on a server).
>>
>> This approach would require a new int field in drm_amdgpu_ctx_in, or
>> repurposing
>> of the flags field.
>>
>> Known current obstacles:
>> ------------------------
>>
>> The SQ is currently programmed to disregard the HQD priorities, and
>> instead it picks
>> jobs at random. Settings from the shader itself are also disregarded
>> as this is
>> considered a privileged field.
>>
>> Effectively we can get our compute wavefront launched ASAP, but we
>> might not get the
>> time we need on the SQ.
>>
>> The current programming would have to be changed to allow priority
>> propagation
>> from the HQD into the SQ.
>>
>> Generic approach for all HW IPs:
>> --------------------------------
>>
>> For consistency purposes, the high priority context can be enabled
>> for all HW IPs
>> with support of the SW scheduler. This will function similarly to the
>> current
>> AMD_SCHED_PRIORITY_KERNEL priority, where the job can jump ahead of
>> anything not
>> commited to the HW queue.
>>
>> The benefits of requesting a high priority context for a non-compute
>> queue will
>> be lesser (e.g. up to 10s of wait time if a GFX command is stuck in
>> front of
>> you), but having the API in place will allow us to easily improve the
>> implementation
>> in the future as new features become available in new hardware.
>>
>> Future steps:
>> -------------
>>
>> Once we have an approach settled, I can take care of the implementation.
>>
>> Also, once the interface is mostly decided, we can start thinking about
>> exposing the high priority queue through radv.
>>
>> Request for feedback:
>> ---------------------
>>
>> We aren't married to any of the approaches outlined above. Our goal
>> is to
>> obtain a mechanism that will allow us to complete the reprojection
>> job within a
>> predictable amount of time. So if anyone anyone has any suggestions for
>> improvements or alternative strategies we are more than happy to hear
>> them.
>>
>> If any of the technical information above is also incorrect, feel
>> free to point
>> out my misunderstandings.
>>
>> Looking forward to hearing from you.
>>
>> Regards,
>> Andres
>>
>> _______________________________________________
>> amd-gfx mailing list
>> amd-gfx at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
>>
>>
>> amd-gfx Info Page - lists.freedesktop.org
>> lists.freedesktop.org
>> To see the collection of prior postings to the list, visit the
>> amd-gfx Archives. Using amd-gfx: To post a message to all the list
>> members, send email ...
>>
>>
>>
>> amd-gfx Info Page - lists.freedesktop.org
>> lists.freedesktop.org
>> To see the collection of prior postings to the list, visit the
>> amd-gfx Archives. Using amd-gfx: To post a message to all the list
>> members, send email ...
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> amd-gfx mailing list
>> amd-gfx at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
>>
>
> _______________________________________________
> amd-gfx mailing list
> amd-gfx at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
