Hi Am 09.09.24 um 07:15 schrieb Yan Zhao:
Use ioremap_wc() instead of ioremap() to map framebuffer during driver probing phase. Using ioremap() results in a VA being mapped with PAT=UC-. Additionally, on x86 architectures, ioremap() invokes memtype_reserve() to reserve the memory type as UC- for the physical range. This reservation can cause subsequent calls to ioremap_wc() to fail to map the VA with PAT=WC to the same physical range for framebuffre in ttm_kmap_iter_linear_io_init(). Consequently, the operation drm_gem_vram_bo_driver_move() -> ttm_bo_move_memcpy() -> ttm_move_memcpy() becomes significantly slow on platforms where UC memory access is slow.
I've noticed this too and pushed a major update that replaces the entire memory management. [1]
The patch is still welcome, I think, but you may want to rebase onto the latest drm-misc-next branch. [2]
Best regards Thomas [1] https://patchwork.freedesktop.org/series/138086/ [2] https://gitlab.freedesktop.org/drm/misc/kernel/-/tree/drm-misc-next
Here's the performance data measured in a guest on the physical machine "Sapphire Rapids XCC". With host KVM honors guest PAT memory types, the effective memory type for this framebuffer range is - WC when ioremap_wc() is used in driver probing phase - UC- when ioremap() is used. The data presented is an average from 10 execution runs. The memcpy range for the data is mem->bus.offset=0xfd000000, mem->size=0x3e8000. -------------------------------------------------------------- | in bochs_hw_init() | | ioremap() | ioremap_wc() | ------------------------------|----------------|--------------| cycles of | 2227.4M | 17.8M | drm_gem_vram_bo_driver_move() | | | ------------------------------|----------------|--------------| time of | 1.24s | 0.01s | drm_gem_vram_bo_driver_move() | | | -------------------------------------------------------------- Reported-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Closes: https://lore.kernel.org/all/87jzfutmfc.fsf@xxxxxxxxxx/#t Cc: Sean Christopherson <seanjc@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Kevin Tian <kevin.tian@xxxxxxxxx> Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx> --- drivers/gpu/drm/tiny/bochs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/tiny/bochs.c b/drivers/gpu/drm/tiny/bochs.c index 31fc5d839e10..6414f0a72f6a 100644 --- a/drivers/gpu/drm/tiny/bochs.c +++ b/drivers/gpu/drm/tiny/bochs.c @@ -261,7 +261,7 @@ static int bochs_hw_init(struct drm_device *dev) if (pci_request_region(pdev, 0, "bochs-drm") != 0) DRM_WARN("Cannot request framebuffer, boot fb still active?\n");- bochs->fb_map = ioremap(addr, size);+ bochs->fb_map = ioremap_wc(addr, size); if (bochs->fb_map == NULL) { DRM_ERROR("Cannot map framebuffer\n"); return -ENOMEM;
-- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)
