Re: [PATCH 7/9] drm/i915/gt: Pipelined page migration

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Tue, 2021-06-08 at 11:28 +0200, Thomas Hellström wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> If we pipeline the PTE updates and then do the copy of those pages
> within a single unpreemptible command packet, we can submit the
> copies
> and leave them to be scheduled without having to synchronously wait
> under a global lock. In order to manage migration, we need to
> preallocate the page tables (and keep them pinned and available for
> use
> at any time), causing a bottleneck for migrations as all clients must
> contend on the limited resources. By inlining the ppGTT updates and
> performing the blit atomically, each client only owns the PTE while
> in
> use, and so we can reschedule individual operations however we see
> fit.
> And most importantly, we do not need to take a global lock on the
> shared
> vm, and wait until the operation is complete before releasing the
> lock
> for others to claim the PTE for themselves.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Co-developed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/Makefile                 |   1 +
>  drivers/gpu/drm/i915/gt/intel_engine.h        |   1 +
>  drivers/gpu/drm/i915/gt/intel_gpu_commands.h  |   2 +
>  drivers/gpu/drm/i915/gt/intel_migrate.c       | 543
> ++++++++++++++++++
>  drivers/gpu/drm/i915/gt/intel_migrate.h       |  45 ++
>  drivers/gpu/drm/i915/gt/intel_migrate_types.h |  15 +
>  drivers/gpu/drm/i915/gt/intel_ring.h          |   1 +
>  drivers/gpu/drm/i915/gt/selftest_migrate.c    | 291 ++++++++++
>  .../drm/i915/selftests/i915_live_selftests.h  |   1 +
>  9 files changed, 900 insertions(+)
>  create mode 100644 drivers/gpu/drm/i915/gt/intel_migrate.c
>  create mode 100644 drivers/gpu/drm/i915/gt/intel_migrate.h
>  create mode 100644 drivers/gpu/drm/i915/gt/intel_migrate_types.h
>  create mode 100644 drivers/gpu/drm/i915/gt/selftest_migrate.c
> 
> diff --git a/drivers/gpu/drm/i915/Makefile
> b/drivers/gpu/drm/i915/Makefile
> index ea8ee4b3e018..9f18902be626 100644
> --- a/drivers/gpu/drm/i915/Makefile
> +++ b/drivers/gpu/drm/i915/Makefile
> @@ -109,6 +109,7 @@ gt-y += \
>         gt/intel_gtt.o \
>         gt/intel_llc.o \
>         gt/intel_lrc.o \
> +       gt/intel_migrate.o \
>         gt/intel_mocs.o \
>         gt/intel_ppgtt.o \
>         gt/intel_rc6.o \
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h
> b/drivers/gpu/drm/i915/gt/intel_engine.h
> index 0862c42b4cac..949965680c37 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> @@ -188,6 +188,7 @@ intel_write_status_page(struct intel_engine_cs
> *engine, int reg, u32 value)
>  #define I915_GEM_HWS_PREEMPT_ADDR      (I915_GEM_HWS_PREEMPT *
> sizeof(u32))
>  #define I915_GEM_HWS_SEQNO             0x40
>  #define I915_GEM_HWS_SEQNO_ADDR                (I915_GEM_HWS_SEQNO *
> sizeof(u32))
> +#define I915_GEM_HWS_MIGRATE           (0x42 * sizeof(u32))
>  #define I915_GEM_HWS_SCRATCH           0x80
>  
>  #define I915_HWS_CSB_BUF0_INDEX                0x10
> diff --git a/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> b/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> index 2694dbb9967e..1c3af0fc0456 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> @@ -123,8 +123,10 @@
>  #define   MI_SEMAPHORE_SAD_NEQ_SDD     (5 << 12)
>  #define   MI_SEMAPHORE_TOKEN_MASK      REG_GENMASK(9, 5)
>  #define   MI_SEMAPHORE_TOKEN_SHIFT     5
> +#define MI_STORE_DATA_IMM      MI_INSTR(0x20, 0)
>  #define MI_STORE_DWORD_IMM     MI_INSTR(0x20, 1)
>  #define MI_STORE_DWORD_IMM_GEN4        MI_INSTR(0x20, 2)
> +#define MI_STORE_QWORD_IMM_GEN8 (MI_INSTR(0x20, 3) | REG_BIT(21))
>  #define   MI_MEM_VIRTUAL       (1 << 22) /* 945,g33,965 */
>  #define   MI_USE_GGTT          (1 << 22) /* g4x+ */
>  #define MI_STORE_DWORD_INDEX   MI_INSTR(0x21, 1)
> diff --git a/drivers/gpu/drm/i915/gt/intel_migrate.c
> b/drivers/gpu/drm/i915/gt/intel_migrate.c
> new file mode 100644
> index 000000000000..1f60f8ee36f8
> --- /dev/null
> +++ b/drivers/gpu/drm/i915/gt/intel_migrate.c
> @@ -0,0 +1,543 @@
> +// SPDX-License-Identifier: MIT
> +/*
> + * Copyright © 2020 Intel Corporation
> + */
> +
> +#include "i915_drv.h"
> +#include "intel_context.h"
> +#include "intel_gpu_commands.h"
> +#include "intel_gt.h"
> +#include "intel_gtt.h"
> +#include "intel_migrate.h"
> +#include "intel_ring.h"
> +
> 
...
> +
> +void intel_migrate_fini(struct intel_migrate *m)
> +{
> +       struct intel_context *ce;
> +
> +       ce = fetch_and_zero(&m->context);
> +       if (!ce)
> +               return;
> +
> +       intel_context_unpin(ce);
> +       intel_context_put(ce);
> +}

Hmm, CI hints at we should be exporting and using an
intel_engine_destroy_pinned_context() here...

/Thomas