On Tue, 8 Jun 2021 at 10:29, Thomas Hellström
<thomas.hellstrom@xxxxxxxxxxxxxxx> wrote:
>
> From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxxx>
> Co-developed-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> ---
> 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"
> +
> +struct insert_pte_data {
> + u64 offset;
> + bool is_lmem;
> +};
> +
> +#define CHUNK_SZ SZ_8M /* ~1ms at 8GiB/s preemption delay */
> +
> +static bool engine_supports_migration(struct intel_engine_cs *engine)
> +{
> + if (!engine)
> + return false;
> +
> + /*
> + * We need the ability to prevent aribtration (MI_ARB_ON_OFF),
> + * the ability to write PTE using inline data (MI_STORE_DATA)
> + * and of course the ability to do the block transfer (blits).
> + */
> + GEM_BUG_ON(engine->class != COPY_ENGINE_CLASS);
> +
> + return true;
> +}
> +
> +static void insert_pte(struct i915_address_space *vm,
> + struct i915_page_table *pt,
> + void *data)
> +{
> + struct insert_pte_data *d = data;
> +
> + vm->insert_page(vm, px_dma(pt), d->offset, I915_CACHE_NONE,
> + d->is_lmem ? PTE_LM : 0);
> + d->offset += PAGE_SIZE;
> +}
> +
> +static struct i915_address_space *migrate_vm(struct intel_gt *gt)
> +{
> + struct i915_vm_pt_stash stash = {};
> + struct i915_ppgtt *vm;
> + int err;
> + int i;
> +
> + /*
> + * We construct a very special VM for use by all migration contexts,
> + * it is kept pinned so that it can be used at any time. As we need
> + * to pre-allocate the page directories for the migration VM, this
> + * limits us to only using a small number of prepared vma.
> + *
> + * To be able to pipeline and reschedule migration operations while
> + * avoiding unnecessary contention on the vm itself, the PTE updates
> + * are inline with the blits. All the blits use the same fixed
> + * addresses, with the backing store redirection being updated on the
> + * fly. Only 2 implicit vma are used for all migration operations.
> + *
> + * We lay the ppGTT out as:
> + *
> + * [0, CHUNK_SZ) -> first object
> + * [CHUNK_SZ, 2 * CHUNK_SZ) -> second object
> + * [2 * CHUNK_SZ, 2 * CHUNK_SZ + 2 * CHUNK_SZ >> 9] -> PTE
> + *
> + * By exposing the dma addresses of the page directories themselves
> + * within the ppGTT, we are then able to rewrite the PTE prior to use.
> + * But the PTE update and subsequent migration operation must be atomic,
> + * i.e. within the same non-preemptible window so that we do not switch
> + * to another migration context that overwrites the PTE.
> + */
> +
> + vm = i915_ppgtt_create(gt);
> + if (IS_ERR(vm))
> + return ERR_CAST(vm);
> +
> + if (!vm->vm.allocate_va_range || !vm->vm.foreach) {
> + err = -ENODEV;
> + goto err_vm;
> + }
> +
> + /*
> + * Each engine instance is assigned its own chunk in the VM, so
> + * that we can run multiple instances concurrently
> + */
> + for (i = 0; i < ARRAY_SIZE(gt->engine_class[COPY_ENGINE_CLASS]); i++) {
> + struct intel_engine_cs *engine;
> + u64 base = (u64)i << 32;
> + struct insert_pte_data d = {};
> + struct i915_gem_ww_ctx ww;
> + u64 sz;
> +
> + engine = gt->engine_class[COPY_ENGINE_CLASS][i];
> + if (!engine_supports_migration(engine))
> + continue;
> +
> + /*
> + * We copy in 8MiB chunks. Each PDE covers 2MiB, so we need
> + * 4x2 page directories for source/destination.
> + */
> + sz = 2 * CHUNK_SZ;
> + d.offset = base + sz;
> +
> + /*
> + * We need another page directory setup so that we can write
> + * the 8x512 PTE in each chunk.
> + */
> + sz += (sz >> 12) * sizeof(u64);
> +
> + err = i915_vm_alloc_pt_stash(&vm->vm, &stash, sz);
> + if (err)
> + goto err_vm;
> +
> + for_i915_gem_ww(&ww, err, true) {
> + err = i915_vm_lock_objects(&vm->vm, &ww);
> + if (err)
> + continue;
> + err = i915_vm_map_pt_stash(&vm->vm, &stash);
> + if (err)
> + continue;
> +
> + vm->vm.allocate_va_range(&vm->vm, &stash, base, base + sz);
> + }
> + i915_vm_free_pt_stash(&vm->vm, &stash);
> + if (err)
> + goto err_vm;
> +
> + /* Now allow the GPU to rewrite the PTE via its own ppGTT */
> + d.is_lmem = i915_gem_object_is_lmem(vm->vm.scratch[0]);
> + vm->vm.foreach(&vm->vm, base, base + sz, insert_pte, &d);
Will this play nice with Xe HP where we have min page size
restrictions for the GTT + lmem? The page-table allocations sidestep
such restrictions since they were previously never inserted into the
GTT. Maybe we need the flat-ppGTT at some point? Perhaps add a TODO or
something?
