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Date:	Sun, 20 Jul 2014 23:03:31 -0400
From:	Jerome Glisse <j.glisse@...il.com>
To:	Oded Gabbay <oded.gabbay@....com>
Cc:	David Airlie <airlied@...ux.ie>,
	Alex Deucher <alexdeucher@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Bridgman <John.Bridgman@....com>,
	Joerg Roedel <joro@...tes.org>,
	Andrew Lewycky <Andrew.Lewycky@....com>,
	Christian König <deathsimple@...afone.de>,
	Michel Dänzer <michel.daenzer@....com>,
	Ben Goz <Ben.Goz@....com>,
	Alexey Skidanov <Alexey.Skidanov@....com>,
	Evgeny Pinchuk <Evgeny.Pinchuk@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2 00/25] AMDKFD kernel driver

On Sun, Jul 20, 2014 at 01:46:53PM -0400, 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@....com>
> 
> 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.
> 
> 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.
> 
> 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).

So i skimmed over the iommu v2 specification and while the iommu v2 claims
to obey the user/supervisor flags of the cpu page table, it does not seems
that this is a property set in the iommu against a pasid (ie is a given
pasid is allow supervisor access or not). It seems that the supervisor is
part of pcie tlp request which i assume is control by the gpu. So how is
this bit set ? How can we make sure that there is no way to abuse it ?

> 
> 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. 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.
> 
> 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@....com>
> > 
> > 
> > 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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