From: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
commit 5207c393d3e7dda9aff813d6b3e2264370d241be upstream.
The caching mode for buffer objects with VRAM as a possible
placement was forced to write-combined, regardless of placement.
However, write-combined system memory is expensive to allocate and
even though it is pooled, the pool is expensive to shrink, since
it involves global CPU TLB flushes.
Moreover write-combined system memory from TTM is only reliably
available on x86 and DGFX doesn't have an x86 restriction.
So regardless of the cpu caching mode selected for a bo,
internally use write-back caching mode for system memory on DGFX.
Coherency is maintained, but user-space clients may perceive a
difference in cpu access speeds.
v2:
- Update RB- and Ack tags.
- Rephrase wording in xe_drm.h (Matt Roper)
v3:
- Really rephrase wording.
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Fixes: 622f709ca629 ("drm/xe/uapi: Add support for CPU caching mode")
Cc: Pallavi Mishra <pallavi.mishra@xxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Effie Yu <effie.yu@xxxxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Jose Souza <jose.souza@xxxxxxxxx>
Cc: Michal Mrozek <michal.mrozek@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v6.8+
Acked-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Acked-by: José Roberto de Souza <jose.souza@xxxxxxxxx>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Fixes: 622f709ca629 ("drm/xe/uapi: Add support for CPU caching mode")
Acked-by: Michal Mrozek <michal.mrozek@xxxxxxxxx>
Acked-by: Effie Yu <effie.yu@xxxxxxxxx> #On chat
Link: https://patchwork.freedesktop.org/patch/msgid/20240705132828.27714-1-thomas.hellstrom@xxxxxxxxxxxxxxx
(cherry picked from commit 01e0cfc994be484ddcb9e121e353e51d8bb837c0)
Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/xe/xe_bo.c | 47 +++++++++++++++++++++++----------------
drivers/gpu/drm/xe/xe_bo_types.h | 3 +-
include/uapi/drm/xe_drm.h | 8 +++++-
3 files changed, 37 insertions(+), 21 deletions(-)
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -317,7 +317,7 @@ static struct ttm_tt *xe_ttm_tt_create(s
struct xe_device *xe = xe_bo_device(bo);
struct xe_ttm_tt *tt;
unsigned long extra_pages;
- enum ttm_caching caching;
+ enum ttm_caching caching = ttm_cached;
int err;
tt = kzalloc(sizeof(*tt), GFP_KERNEL);
@@ -331,26 +331,35 @@ static struct ttm_tt *xe_ttm_tt_create(s
extra_pages = DIV_ROUND_UP(xe_device_ccs_bytes(xe, bo->size),
PAGE_SIZE);
- switch (bo->cpu_caching) {
- case DRM_XE_GEM_CPU_CACHING_WC:
- caching = ttm_write_combined;
- break;
- default:
- caching = ttm_cached;
- break;
- }
-
- WARN_ON((bo->flags & XE_BO_FLAG_USER) && !bo->cpu_caching);
-
/*
- * Display scanout is always non-coherent with the CPU cache.
- *
- * For Xe_LPG and beyond, PPGTT PTE lookups are also non-coherent and
- * require a CPU:WC mapping.
+ * DGFX system memory is always WB / ttm_cached, since
+ * other caching modes are only supported on x86. DGFX
+ * GPU system memory accesses are always coherent with the
+ * CPU.
*/
- if ((!bo->cpu_caching && bo->flags & XE_BO_FLAG_SCANOUT) ||
- (xe->info.graphics_verx100 >= 1270 && bo->flags & XE_BO_FLAG_PAGETABLE))
- caching = ttm_write_combined;
+ if (!IS_DGFX(xe)) {
+ switch (bo->cpu_caching) {
+ case DRM_XE_GEM_CPU_CACHING_WC:
+ caching = ttm_write_combined;
+ break;
+ default:
+ caching = ttm_cached;
+ break;
+ }
+
+ WARN_ON((bo->flags & XE_BO_FLAG_USER) && !bo->cpu_caching);
+
+ /*
+ * Display scanout is always non-coherent with the CPU cache.
+ *
+ * For Xe_LPG and beyond, PPGTT PTE lookups are also
+ * non-coherent and require a CPU:WC mapping.
+ */
+ if ((!bo->cpu_caching && bo->flags & XE_BO_FLAG_SCANOUT) ||
+ (xe->info.graphics_verx100 >= 1270 &&
+ bo->flags & XE_BO_FLAG_PAGETABLE))
+ caching = ttm_write_combined;
+ }
err = ttm_tt_init(&tt->ttm, &bo->ttm, page_flags, caching, extra_pages);
if (err) {
--- a/drivers/gpu/drm/xe/xe_bo_types.h
+++ b/drivers/gpu/drm/xe/xe_bo_types.h
@@ -66,7 +66,8 @@ struct xe_bo {
/**
* @cpu_caching: CPU caching mode. Currently only used for userspace
- * objects.
+ * objects. Exceptions are system memory on DGFX, which is always
+ * WB.
*/
u16 cpu_caching;
--- a/include/uapi/drm/xe_drm.h
+++ b/include/uapi/drm/xe_drm.h
@@ -776,7 +776,13 @@ struct drm_xe_gem_create {
#define DRM_XE_GEM_CPU_CACHING_WC 2
/**
* @cpu_caching: The CPU caching mode to select for this object. If
- * mmaping the object the mode selected here will also be used.
+ * mmaping the object the mode selected here will also be used. The
+ * exception is when mapping system memory (including data evicted
+ * to system) on discrete GPUs. The caching mode selected will
+ * then be overridden to DRM_XE_GEM_CPU_CACHING_WB, and coherency
+ * between GPU- and CPU is guaranteed. The caching mode of
+ * existing CPU-mappings will be updated transparently to
+ * user-space clients.
*/
__u16 cpu_caching;
/** @pad: MBZ */
Patches currently in stable-queue which might be from thomas.hellstrom@xxxxxxxxxxxxxxx are
queue-6.10/drm-xe-use-write-back-caching-mode-for-system-memory-on-dgfx.patch
queue-6.10/drm-ttm-tests-fix-a-warning-in-ttm_bo_unreserve_bulk.patch
