| Message ID | 20240619163904.2935-1-thomas.hellstrom@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/xe: Use write-back caching mode for system memory on DGFX | expand |
On 19/06/2024 17:39, Thomas Hellström wrote: > 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. > > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com> > Fixes: 622f709ca629 ("drm/xe/uapi: Add support for CPU caching mode") > Cc: Pallavi Mishra <pallavi.mishra@intel.com> > Cc: Matthew Auld <matthew.auld@intel.com> > Cc: dri-devel@lists.freedesktop.org > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> > Cc: Effie Yu <effie.yu@intel.com> > Cc: Matthew Brost <matthew.brost@intel.com> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > Cc: Jose Souza <jose.souza@intel.com> > Cc: Michal Mrozek <michal.mrozek@intel.com> > Cc: <stable@vger.kernel.org> # v6.8+ Acked-by: Matthew Auld <matthew.auld@intel.com> > --- > 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(-) > > diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c > index 65c696966e96..31192d983d9e 100644 > --- a/drivers/gpu/drm/xe/xe_bo.c > +++ b/drivers/gpu/drm/xe/xe_bo.c > @@ -343,7 +343,7 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo, > 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); > @@ -357,26 +357,35 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo, > 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; > + } > > if (bo->flags & XE_BO_FLAG_NEEDS_UC) { > /* > diff --git a/drivers/gpu/drm/xe/xe_bo_types.h b/drivers/gpu/drm/xe/xe_bo_types.h > index 86422e113d39..10450f1fbbde 100644 > --- 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; > > diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h > index 93e00be44b2d..1189b3044723 100644 > --- a/include/uapi/drm/xe_drm.h > +++ b/include/uapi/drm/xe_drm.h > @@ -783,7 +783,13 @@ 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 evicted > + * system memory) 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 */
On Wed, Jun 19, 2024 at 06:39:04PM +0200, Thomas Hellström wrote: > 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. > > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com> > Fixes: 622f709ca629 ("drm/xe/uapi: Add support for CPU caching mode") > Cc: Pallavi Mishra <pallavi.mishra@intel.com> > Cc: Matthew Auld <matthew.auld@intel.com> > Cc: dri-devel@lists.freedesktop.org > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> > Cc: Effie Yu <effie.yu@intel.com> > Cc: Matthew Brost <matthew.brost@intel.com> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > Cc: Jose Souza <jose.souza@intel.com> > Cc: Michal Mrozek <michal.mrozek@intel.com> > Cc: <stable@vger.kernel.org> # v6.8+ > --- > 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(-) > > diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c > index 65c696966e96..31192d983d9e 100644 > --- a/drivers/gpu/drm/xe/xe_bo.c > +++ b/drivers/gpu/drm/xe/xe_bo.c > @@ -343,7 +343,7 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo, > 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); > @@ -357,26 +357,35 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo, > 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; > + } > > if (bo->flags & XE_BO_FLAG_NEEDS_UC) { > /* > diff --git a/drivers/gpu/drm/xe/xe_bo_types.h b/drivers/gpu/drm/xe/xe_bo_types.h > index 86422e113d39..10450f1fbbde 100644 > --- 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; > > diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h > index 93e00be44b2d..1189b3044723 100644 > --- a/include/uapi/drm/xe_drm.h > +++ b/include/uapi/drm/xe_drm.h > @@ -783,7 +783,13 @@ 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 evicted > + * system memory) on discrete GPUs. The caching mode selected will Was this supposed to say "including evicted vram?" Matt > + * 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 */ > -- > 2.44.0 >
diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c index 65c696966e96..31192d983d9e 100644 --- a/drivers/gpu/drm/xe/xe_bo.c +++ b/drivers/gpu/drm/xe/xe_bo.c @@ -343,7 +343,7 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo, 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); @@ -357,26 +357,35 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo, 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; + } if (bo->flags & XE_BO_FLAG_NEEDS_UC) { /* diff --git a/drivers/gpu/drm/xe/xe_bo_types.h b/drivers/gpu/drm/xe/xe_bo_types.h index 86422e113d39..10450f1fbbde 100644 --- 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; diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h index 93e00be44b2d..1189b3044723 100644 --- a/include/uapi/drm/xe_drm.h +++ b/include/uapi/drm/xe_drm.h @@ -783,7 +783,13 @@ 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 evicted + * system memory) 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 */
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. Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com> Fixes: 622f709ca629 ("drm/xe/uapi: Add support for CPU caching mode") Cc: Pallavi Mishra <pallavi.mishra@intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: dri-devel@lists.freedesktop.org Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Effie Yu <effie.yu@intel.com> Cc: Matthew Brost <matthew.brost@intel.com> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Cc: Jose Souza <jose.souza@intel.com> Cc: Michal Mrozek <michal.mrozek@intel.com> Cc: <stable@vger.kernel.org> # v6.8+ --- 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(-)