Re: [PATCH v2 00/25] AMDKFD kernel driver

[Jerome Glisse]

On Mon, Jul 21, 2014 at 05:12:06PM +0300, Oded Gabbay wrote:
> On 21/07/14 16:39, Christian König wrote:
> >Am 21.07.2014 14:36, schrieb Oded Gabbay:
> >>On 20/07/14 20:46, Jerome Glisse wrote:
> >>>On Thu, Jul 17, 2014 at 04:57:25PM +0300, Oded Gabbay wrote:
> >>>>Forgot to cc mailing list on cover letter. Sorry.
> >>>>
> >>>>As a continuation to the existing discussion, here is a v2 patch series
> >>>>restructured with a cleaner history and no totally-different-early-versions
> >>>>of the code.
> >>>>
> >>>>Instead of 83 patches, there are now a total of 25 patches, where 5 of them
> >>>>are modifications to radeon driver and 18 of them include only amdkfd code.
> >>>>There is no code going away or even modified between patches, only added.
> >>>>
> >>>>The driver was renamed from radeon_kfd to amdkfd and moved to reside under
> >>>>drm/radeon/amdkfd. This move was done to emphasize the fact that this driver
> >>>>is an AMD-only driver at this point. Having said that, we do foresee a
> >>>>generic hsa framework being implemented in the future and in that case, we
> >>>>will adjust amdkfd to work within that framework.
> >>>>
> >>>>As the amdkfd driver should support multiple AMD gfx drivers, we want to
> >>>>keep it as a seperate driver from radeon. Therefore, the amdkfd code is
> >>>>contained in its own folder. The amdkfd folder was put under the radeon
> >>>>folder because the only AMD gfx driver in the Linux kernel at this point
> >>>>is the radeon driver. Having said that, we will probably need to move it
> >>>>(maybe to be directly under drm) after we integrate with additional AMD gfx
> >>>>drivers.
> >>>>
> >>>>For people who like to review using git, the v2 patch set is located at:
> >>>>http://cgit.freedesktop.org/~gabbayo/linux/log/?h=kfd-next-3.17-v2
> >>>>
> >>>>Written by Oded Gabbayh <oded.gabbay@xxxxxxx>
> >>>
> >>>So quick comments before i finish going over all patches. There is many
> >>>things that need more documentation espacialy as of right now there is
> >>>no userspace i can go look at.
> >>So quick comments on some of your questions but first of all, thanks for the
> >>time you dedicated to review the code.
> >>>
> >>>There few show stopper, biggest one is gpu memory pinning this is a big
> >>>no, that would need serious arguments for any hope of convincing me on
> >>>that side.
> >>We only do gpu memory pinning for kernel objects. There are no userspace
> >>objects that are pinned on the gpu memory in our driver. If that is the case,
> >>is it still a show stopper ?
> >>
> >>The kernel objects are:
> >>- pipelines (4 per device)
> >>- mqd per hiq (only 1 per device)
> >>- mqd per userspace queue. On KV, we support up to 1K queues per process, for
> >>a total of 512K queues. Each mqd is 151 bytes, but the allocation is done in
> >>256 alignment. So total *possible* memory is 128MB
> >>- kernel queue (only 1 per device)
> >>- fence address for kernel queue
> >>- runlists for the CP (1 or 2 per device)
> >
> >The main questions here are if it's avoid able to pin down the memory and if the
> >memory is pinned down at driver load, by request from userspace or by anything
> >else.
> >
> >As far as I can see only the "mqd per userspace queue" might be a bit
> >questionable, everything else sounds reasonable.
> >
> >Christian.
> 
> Most of the pin downs are done on device initialization.
> The "mqd per userspace" is done per userspace queue creation. However, as I
> said, it has an upper limit of 128MB on KV, and considering the 2G local
> memory, I think it is OK.
> The runlists are also done on userspace queue creation/deletion, but we only
> have 1 or 2 runlists per device, so it is not that bad.

2G local memory ? You can not assume anything on userside configuration some
one might build an hsa computer with 512M and still expect a functioning
desktop.

I need to go look into what all this mqd is for, what it does and what it is
about. But pinning is really bad and this is an issue with userspace command
scheduling an issue that obviously AMD fails to take into account in design
phase.

> 	Oded
> >
> >>>
> >>>It might be better to add a drivers/gpu/drm/amd directory and add common
> >>>stuff there.
> >>>
> >>>Given that this is not intended to be final HSA api AFAICT then i would
> >>>say this far better to avoid the whole kfd module and add ioctl to radeon.
> >>>This would avoid crazy communication btw radeon and kfd.
> >>>
> >>>The whole aperture business needs some serious explanation. Especialy as
> >>>you want to use userspace address there is nothing to prevent userspace
> >>>program from allocating things at address you reserve for lds, scratch,
> >>>... only sane way would be to move those lds, scratch inside the virtual
> >>>address reserved for kernel (see kernel memory map).
> >>>
> >>>The whole business of locking performance counter for exclusive per process
> >>>access is a big NO. Which leads me to the questionable usefullness of user
> >>>space command ring.
> >>That's like saying: "Which leads me to the questionable usefulness of HSA". I
> >>find it analogous to a situation where a network maintainer nacking a driver
> >>for a network card, which is slower than a different network card. Doesn't
> >>seem reasonable this situation is would happen. He would still put both the
> >>drivers in the kernel because people want to use the H/W and its features. So,
> >>I don't think this is a valid reason to NACK the driver.

Let me rephrase, drop the the performance counter ioctl and modulo memory pinning
i see no objection. In other word, i am not NACKING whole patchset i am NACKING
the performance ioctl.

Again this is another argument for round trip to the kernel. As inside kernel you
could properly do exclusive gpu counter access accross single user cmd buffer
execution.

> >>
> >>>I only see issues with that. First and foremost i would
> >>>need to see solid figures that kernel ioctl or syscall has a higher an
> >>>overhead that is measurable in any meaning full way against a simple
> >>>function call. I know the userspace command ring is a big marketing features
> >>>that please ignorant userspace programmer. But really this only brings issues
> >>>and for absolutely not upside afaict.
> >>Really ? You think that doing a context switch to kernel space, with all its
> >>overhead, is _not_ more expansive than just calling a function in userspace
> >>which only puts a buffer on a ring and writes a doorbell ?

I am saying the overhead is not that big and it probably will not matter in most
usecase. For instance i did wrote the most useless kernel module that add two
number through an ioctl (http://people.freedesktop.org/~glisse/adder.tar) and
it takes ~0.35microseconds with ioctl while function is ~0.025microseconds so
ioctl is 13 times slower.

Now if there is enough data that shows that a significant percentage of jobs
submited to the GPU will take less that 0.35microsecond then yes userspace
scheduling does make sense. But so far all we have is handwaving with no data
to support any facts.


Now if we want to schedule from userspace than you will need to do something
about the pinning, something that gives control to kernel so that kernel can
unpin when it wants and move object when it wants no matter what userspace is
doing.

> >>>
> >>>So i would rather see a very simple ioctl that write the doorbell and might
> >>>do more than that in case of ring/queue overcommit where it would first have
> >>>to wait for a free ring/queue to schedule stuff. This would also allow sane
> >>>implementation of things like performance counter that could be acquire by
> >>>kernel for duration of a job submitted by userspace. While still not optimal
> >>>this would be better that userspace locking.
> >>>
> >>>
> >>>I might have more thoughts once i am done with all the patches.
> >>>
> >>>Cheers,
> >>>Jérôme
> >>>
> >>>>
> >>>>Original Cover Letter:
> >>>>
> >>>>This patch set implements a Heterogeneous System Architecture (HSA) driver
> >>>>for radeon-family GPUs.
> >>>>HSA allows different processor types (CPUs, DSPs, GPUs, etc..) to share
> >>>>system resources more effectively via HW features including shared pageable
> >>>>memory, userspace-accessible work queues, and platform-level atomics. In
> >>>>addition to the memory protection mechanisms in GPUVM and IOMMUv2, the Sea
> >>>>Islands family of GPUs also performs HW-level validation of commands passed
> >>>>in through the queues (aka rings).
> >>>>
> >>>>The code in this patch set is intended to serve both as a sample driver for
> >>>>other HSA-compatible hardware devices and as a production driver for
> >>>>radeon-family processors. The code is architected to support multiple CPUs
> >>>>each with connected GPUs, although the current implementation focuses on a
> >>>>single Kaveri/Berlin APU, and works alongside the existing radeon kernel
> >>>>graphics driver (kgd).
> >>>>AMD GPUs designed for use with HSA (Sea Islands and up) share some hardware
> >>>>functionality between HSA compute and regular gfx/compute (memory,
> >>>>interrupts, registers), while other functionality has been added
> >>>>specifically for HSA compute  (hw scheduler for virtualized compute rings).
> >>>>All shared hardware is owned by the radeon graphics driver, and an interface
> >>>>between kfd and kgd allows the kfd to make use of those shared resources,
> >>>>while HSA-specific functionality is managed directly by kfd by submitting
> >>>>packets into an HSA-specific command queue (the "HIQ").
> >>>>
> >>>>During kfd module initialization a char device node (/dev/kfd) is created
> >>>>(surviving until module exit), with ioctls for queue creation & management,
> >>>>and data structures are initialized for managing HSA device topology.
> >>>>The rest of the initialization is driven by calls from the radeon kgd at the
> >>>>following points :
> >>>>
> >>>>- radeon_init (kfd_init)
> >>>>- radeon_exit (kfd_fini)
> >>>>- radeon_driver_load_kms (kfd_device_probe, kfd_device_init)
> >>>>- radeon_driver_unload_kms (kfd_device_fini)
> >>>>
> >>>>During the probe and init processing per-device data structures are
> >>>>established which connect to the associated graphics kernel driver. This
> >>>>information is exposed to userspace via sysfs, along with a version number
> >>>>allowing userspace to determine if a topology change has occurred while it
> >>>>was reading from sysfs.
> >>>>The interface between kfd and kgd also allows the kfd to request buffer
> >>>>management services from kgd, and allows kgd to route interrupt requests to
> >>>>kfd code since the interrupt block is shared between regular
> >>>>graphics/compute and HSA compute subsystems in the GPU.
> >>>>
> >>>>The kfd code works with an open source usermode library ("libhsakmt") which
> >>>>is in the final stages of IP review and should be published in a separate
> >>>>repo over the next few days.
> >>>>The code operates in one of three modes, selectable via the sched_policy
> >>>>module parameter :
> >>>>
> >>>>- sched_policy=0 uses a hardware scheduler running in the MEC block within
> >>>>CP, and allows oversubscription (more queues than HW slots)
> >>>>- sched_policy=1 also uses HW scheduling but does not allow
> >>>>oversubscription, so create_queue requests fail when we run out of HW slots
> >>>>- sched_policy=2 does not use HW scheduling, so the driver manually assigns
> >>>>queues to HW slots by programming registers
> >>>>
> >>>>The "no HW scheduling" option is for debug & new hardware bringup only, so
> >>>>has less test coverage than the other options. Default in the current code
> >>>>is "HW scheduling without oversubscription" since that is where we have the
> >>>>most test coverage but we expect to change the default to "HW scheduling
> >>>>with oversubscription" after further testing. This effectively removes the
> >>>>HW limit on the number of work queues available to applications.
> >>>>
> >>>>Programs running on the GPU are associated with an address space through the
> >>>>VMID field, which is translated to a unique PASID at access time via a set
> >>>>of 16 VMID-to-PASID mapping registers. The available VMIDs (currently 16)
> >>>>are partitioned (under control of the radeon kgd) between current
> >>>>gfx/compute and HSA compute, with each getting 8 in the current code. The
> >>>>VMID-to-PASID mapping registers are updated by the HW scheduler when used,
> >>>>and by driver code if HW scheduling is not being used.
> >>>>The Sea Islands compute queues use a new "doorbell" mechanism instead of the
> >>>>earlier kernel-managed write pointer registers. Doorbells use a separate BAR
> >>>>dedicated for this purpose, and pages within the doorbell aperture are
> >>>>mapped to userspace (each page mapped to only one user address space).
> >>>>Writes to the doorbell aperture are intercepted by GPU hardware, allowing
> >>>>userspace code to safely manage work queues (rings) without requiring a
> >>>>kernel call for every ring update.
> >>>>First step for an application process is to open the kfd device. Calls to
> >>>>open create a kfd "process" structure only for the first thread of the
> >>>>process. Subsequent open calls are checked to see if they are from processes
> >>>>using the same mm_struct and, if so, don't do anything. The kfd per-process
> >>>>data lives as long as the mm_struct exists. Each mm_struct is associated
> >>>>with a unique PASID, allowing the IOMMUv2 to make userspace process memory
> >>>>accessible to the GPU.
> >>>>Next step is for the application to collect topology information via sysfs.
> >>>>This gives userspace enough information to be able to identify specific
> >>>>nodes (processors) in subsequent queue management calls. Application
> >>>>processes can create queues on multiple processors, and processors support
> >>>>queues from multiple processes.
> >>>>At this point the application can create work queues in userspace memory and
> >>>>pass them through the usermode library to kfd to have them mapped onto HW
> >>>>queue slots so that commands written to the queues can be executed by the
> >>>>GPU. Queue operations specify a processor node, and so the bulk of this code
> >>>>is device-specific.
> >>>>Written by John Bridgman <John.Bridgman@xxxxxxx>
> >>>>
> >>>>
> >>>>Alexey Skidanov (1):
> >>>>   amdkfd: Implement the Get Process Aperture IOCTL
> >>>>
> >>>>Andrew Lewycky (3):
> >>>>   amdkfd: Add basic modules to amdkfd
> >>>>   amdkfd: Add interrupt handling module
> >>>>   amdkfd: Implement the Set Memory Policy IOCTL
> >>>>
> >>>>Ben Goz (8):
> >>>>   amdkfd: Add queue module
> >>>>   amdkfd: Add mqd_manager module
> >>>>   amdkfd: Add kernel queue module
> >>>>   amdkfd: Add module parameter of scheduling policy
> >>>>   amdkfd: Add packet manager module
> >>>>   amdkfd: Add process queue manager module
> >>>>   amdkfd: Add device queue manager module
> >>>>   amdkfd: Implement the create/destroy/update queue IOCTLs
> >>>>
> >>>>Evgeny Pinchuk (3):
> >>>>   amdkfd: Add topology module to amdkfd
> >>>>   amdkfd: Implement the Get Clock Counters IOCTL
> >>>>   amdkfd: Implement the PMC Acquire/Release IOCTLs
> >>>>
> >>>>Oded Gabbay (10):
> >>>>   mm: Add kfd_process pointer to mm_struct
> >>>>   drm/radeon: reduce number of free VMIDs and pipes in KV
> >>>>   drm/radeon/cik: Don't touch int of pipes 1-7
> >>>>   drm/radeon: Report doorbell configuration to amdkfd
> >>>>   drm/radeon: adding synchronization for GRBM GFX
> >>>>   drm/radeon: Add radeon <--> amdkfd interface
> >>>>   Update MAINTAINERS and CREDITS files with amdkfd info
> >>>>   amdkfd: Add IOCTL set definitions of amdkfd
> >>>>   amdkfd: Add amdkfd skeleton driver
> >>>>   amdkfd: Add binding/unbinding calls to amd_iommu driver
> >>>>
> >>>>  CREDITS                                            |    7 +
> >>>>  MAINTAINERS                                        |   10 +
> >>>>  drivers/gpu/drm/radeon/Kconfig                     |    2 +
> >>>>  drivers/gpu/drm/radeon/Makefile                    |    3 +
> >>>>  drivers/gpu/drm/radeon/amdkfd/Kconfig              |   10 +
> >>>>  drivers/gpu/drm/radeon/amdkfd/Makefile             |   14 +
> >>>>  drivers/gpu/drm/radeon/amdkfd/cik_mqds.h           |  185 +++
> >>>>  drivers/gpu/drm/radeon/amdkfd/cik_regs.h           |  220 ++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_aperture.c       |  123 ++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_chardev.c        |  518 +++++++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_crat.h           |  294 +++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_device.c         |  254 ++++
> >>>>  .../drm/radeon/amdkfd/kfd_device_queue_manager.c   |  985 ++++++++++++++++
> >>>>  .../drm/radeon/amdkfd/kfd_device_queue_manager.h   |  101 ++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_doorbell.c       |  264 +++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_interrupt.c      |  161 +++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_kernel_queue.c   |  305 +++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_kernel_queue.h   |   66 ++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_module.c         |  131 +++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_mqd_manager.c    |  291 +++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_mqd_manager.h    |   54 +
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_packet_manager.c |  488 ++++++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_pasid.c          |   97 ++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_pm4_headers.h    |  682 +++++++++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_pm4_opcodes.h    |  107 ++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_priv.h           |  466 ++++++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_process.c        |  405 +++++++
> >>>>  .../drm/radeon/amdkfd/kfd_process_queue_manager.c  |  343 ++++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_queue.c          |  109 ++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_topology.c       | 1207
> >>>>++++++++++++++++++++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_topology.h       |  168 +++
> >>>>  drivers/gpu/drm/radeon/amdkfd/kfd_vidmem.c         |   96 ++
> >>>>  drivers/gpu/drm/radeon/cik.c                       |  154 +--
> >>>>  drivers/gpu/drm/radeon/cik_reg.h                   |   65 ++
> >>>>  drivers/gpu/drm/radeon/cikd.h                      |   51 +-
> >>>>  drivers/gpu/drm/radeon/radeon.h                    |    9 +
> >>>>  drivers/gpu/drm/radeon/radeon_device.c             |   32 +
> >>>>  drivers/gpu/drm/radeon/radeon_drv.c                |    5 +
> >>>>  drivers/gpu/drm/radeon/radeon_kfd.c                |  566 +++++++++
> >>>>  drivers/gpu/drm/radeon/radeon_kfd.h                |  119 ++
> >>>>  drivers/gpu/drm/radeon/radeon_kms.c                |    7 +
> >>>>  include/linux/mm_types.h                           |   14 +
> >>>>  include/uapi/linux/kfd_ioctl.h                     |  133 +++
> >>>>  43 files changed, 9226 insertions(+), 95 deletions(-)
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/Kconfig
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/Makefile
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/cik_mqds.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/cik_regs.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_aperture.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_chardev.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_crat.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_device.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_device_queue_manager.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_device_queue_manager.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_doorbell.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_interrupt.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_kernel_queue.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_kernel_queue.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_module.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_mqd_manager.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_mqd_manager.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_packet_manager.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_pasid.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_pm4_headers.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_pm4_opcodes.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_priv.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_process.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_process_queue_manager.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_queue.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_topology.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_topology.h
> >>>>  create mode 100644 drivers/gpu/drm/radeon/amdkfd/kfd_vidmem.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/radeon_kfd.c
> >>>>  create mode 100644 drivers/gpu/drm/radeon/radeon_kfd.h
> >>>>  create mode 100644 include/uapi/linux/kfd_ioctl.h
> >>>>
> >>>>--
> >>>>1.9.1
> >>>>
> >>
> >
> 
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